When Colin Creevey is attacked trying to sneak to the hospital wing to see Harry and he´s taken there Dumbledore tells McGonagall, when she asks who may have opened the Chamber: "The question is not who, the question is how..."
Does this mean he knows of the existence of the diary?? Or that the only person who would be able to open it is Riddle??

I think Dumbledore always knew that Tom Riddle was the person who could open the Chamber of secrets the last time and in Harry’s second year. After all Tom Riddle tells Harry when he enters the chamber that,
‘Only the transfiguration teacher, Dumbledore seemed to think Hagrid was innocent. He persuaded Dippet to keep Hagrid and train him as a games Keeper, Yes I think Dumbledore might have guessed.'
Tom also goes on to say Dumbledore kept an annoyingly close watch on him, after Hagrid was expelled.

This suggests that Dumbledore knew that Tom as the only 'the heir of Slytherin could open the Chamber.

I don’t think this means he knew however about Toms diary as he asks Mcgonagoll how Tom opened the chamber, therefore he must not know about the Diary.

Also when Dumbledore is talking to Harry about the diary describe Tom's diary as 'brilliant' when examining it. This also shows us that Dumbledore probably had no prior knowledge of the diary.

Yap! I agree to that, souljacker...

And besides if DD knew about the diary, he wouldn't be surprise to see that the chamber has been reopened.

"The question is not who..."
He knew it was Tom Riddle all along but without any concrete proof. Probably he's excellent in Occlumency and Tom Riddle haven't mastered that skill yet?

"the question is how..."
Supposedly, Tom Riddle is dead, or so to say LV is dead. He's curious how LV after that incident in SS/PS still manage to get inside Hogwarts AND reopened the chamber. He's barely a spirit then... so, how indeed did he managed to open the chamber...

If he knew about the diary... he wouldn't be so clueless, don't you think?

Dumbledore knew. Oh, yes he did know. Take this into consideration if you don't agree. There is a very, very short list of stone turners in the magical world, Dumbledore knows that Tom Riddle is the heir of Slytherin, thereby giving him the power of being a Parselmouth, and Dumbledore has had fifty years to sit on this. The real question was how.

But how did Dumbledore not know how? He knows just about everything that goes on in Hogwarts. I'll give you a clue. The only thing Dumbledore is truly unsure of is Harry's connection to Voldy. Dumbledore is scared of Harry being the one who attacked the students/cat/ghost, but that it is not Harry who is responsible. Let's do a little background check.

Dumbledore has no clue what really happened at Godric's Hollow other than the fact that Lily and James died at the hand of Voldy and the curse rebounded on him when he tried it on Harry. Will this form a connection between Harry and Voldy? Has it already? Does Voldy know about it? Dumbledore took a big risk telling Harry how the Mirror of Erised works. Let's say he was testing Harry to see if the connection had affected his good-evil levels. Judging by what happened during the conversation at the end of PS/SS, we can safely say that Dumbledore now trusts Harry's judgement completely.

I said Harry's, not Voldy's.

Now people are getting petrified. Dumbledore knows Legilimency so he knows that Harry is hiding something. He doesn't like to intrude on other people's minds. He likes to let them tell him about it by their own will. Harry is found at the scene of the crime more than once and he's not telling something to Dumbledore. Is Voldy possesing him? Was he in the wrong place at the wrong time? Could Voldy have possibly given him the power of being a Parselmouth and Harry just heard the snake?

Dumbledore has all this going through his head now. He hears about the dueling club that Lockhart and Snape are setting up, and since he trusts Snape way more, he tells him just enough to let him on to the idea of Harry being able to talk to snakes. Snape takes this into consideration, forms an idea to find out for sure, and proves that Harry is indeed a Parselmouth in the most public and negative way possible.

Although Dumbledore was not pleased with Snape, there you have it. A good thought out thought process on the side of Dumbledore about how, not who, the Chamber of Secrets was opened. He probably didn't know for sure until Harry brought in the diary, but by the time of the dueling club, Dumbledore knew that Harry was not the one responsible.

Like zrya said, Dumbledore always knew it was Tom Riddle. But because he was suppose to be all weak and living far away, he couldn't figure out how he was doing it. My only question is, what would have happened if Riddle had succeeded and comeback. What would have happened between the two Voldemorts?

I don´t think DD told Snape before the duelling club about the posibility of Harry beiung a Parselmouth, no matter how much he trusts him. Besides, the one who conjures the snake is Draco, not Snape.

Bandoth - yet again, another very well thought out and presented theory that fits right in with the changeling hypothesis. Very good...I hadn't thought about it like that. I agree with you about Dumbledore possibly suspecting Harry for a time - the parallel he draws between Tom and Harry by asking them both the same question - 'Do you have something you wish to tell me?' - is undeniable. Perhaps not strictly canon, but did you see the look on Dumbledore's face as Harry left his office? It definitely looked like anxiety and disappointment to me. Why did Chris Columbus keep the shot on his face if his expression wasn't important?

And we all know of this strange relationship between Snape and Dumbledore, most likely related to the secret reason why Snape left the DE's. I find it perfectly plausible that Dumbledore would 'drop hints' to Snape about triggering Harry's latent abilities. And yep, zyra, you were right - Snape did whisper something in Draco's ear before he produced the snake. I think that JKR hid it very cleverly by making it appear as though Snape and Draco were sharing the joke about Lockheart dropping his wand, but I think it would be a mistake to overlook the basic fact that Snape whispered something to Draco that was never clarified.

After reading that fic I've been banging on about for weeks that managed to create such an excellent characterisation of Snape, I've seen him in a whole new way and I really believe that he knows exactly what's going because Dumbledore has told him if not quite everything, then most of it and because of Snape's intense dislike for Harry, it would fit his personality very well to try to humiliate Harry in public - most specifically by forcing him publically to show that he is a parselmouth. No doubt he caught it in the butt from Dumbledore later on, but I still think that Bandoth was right in his suggestions.

But yes, I've wondered what would have happened had the two Voldemort's come together too. But if you view Voldemort as an entity born of Tom Riddle - neither can exist without the other (ooh...echoes of the prophecy there ). If Tom and his memories came back, then the 'essence' that is Voldemort should be able to have rejoined with Tom, shouldn't it?

JK has said when answering FAQ's in her webpage that if Riddle had got out of the diary, he would have made Voldemort stronger, but also said she couldn´t say anything more.

this is a very good question, a very good question, dumbledore is a very powerful and a very smart man. you know it is possible that he knew it was riddle because it says from the book that dombledore kept an anoingly close watch on riddle after he framed harry.


swirlctw

of course he knows about the diary he knows all about lv's life, and he let the whole thing play through so harry could learn not everything is easy

I think Dumbledore knew that Tom Marvolo Riddle was the person who opened the Chamber of Secrets,and I also think that Dumbledore knew what kind of object was used to open it.Besides,I think he already was looking for the horcruxes because he wasn't surprised when Harry gave him the Diary.

I disagree, Horavlo. I think Harry gave DD the idea after he saw the diary Harry had destroyed... it had acted as a human... humans have souls.. it was Voldemort's... and DD was on the path to HBP where he tells Harry all about the Horcruxes.

i agree with Souljacker you pretty much summed it all up well! (good job)

I would like to add that when DD saw the diary it more or less confirmed his theory about the horcruxes. i think that DD had been working to prove that his horcruxe theory was true and i think that that was what he suspected was opening the COS but i dont think he knew it was a diary exactly