See below posts. Im not about to break my warranty and rip of the heatsink to put a Lasagna cooler on there, cause if this problem isn't fixed, I'm most definately going to request a full refund. Making it uglier seems to help unfortunately. Get the drivers 6076 or newer. The heatsink is more than enough unless you overclock higher than the card's specifications.
Heat is a non-issue with the card.
On a different note, you should have proper case ventilation regardless of the situation. I have unbearable control problems when I play a game. There is delay from the time I move the mouse or hit a key, to what actually happens on the screen. Games are unplayable like this. Install the newest drivers and also make sure that V-Sync is not disabled if you are having problems.