My son recently complained that IE started crashing whenever he tried to run Youtube in HD. If he starts playing in 480 and switches to either 720p or 1080p, it starts to play then locks up (yes, the buffer is sufficiently full) and IE crashes. ATI drivers are up to date, and I opened IE in private browsing to disable add-ons, but it didn't make any difference.
Have no idea if this is related, but I installed Chrome to see if the Youtube problem was specific to IE, but then Chrome basically wouldn't run. It opens, but takes absolutely forever just to load the Google page (or any other page I try to go to). In comparison, IE opens right up. Never seen anything like it.
No, my son's running Win 7 Pro 64 bit, also a C2D, 8GB RAM, Radeon HD 6850 - he uses it primarily for gaming, for which it still serves pretty well. Other than Youtube in HD, IE runs fine, which is why I never bothered installing Chrome until now. But, as I indicated, Chrome barely seems to run at all, although I suspect that's a separate issue.