pcfixed its more a poor package/implementation issue with the bga, rather then heating etc, although heat just makes the issue worse (hot cold, flex from the fact that its flexing in the laptop too etc), and i have managed to obtain a Dell 9400 with a 7900GS video card (for nothing) and reflow'd it (along with fixing the common sound cut out issue) and it has been lasting me a good year now atleast (good for a free unit). In theory because of a decent reflow job the chip would actually sink lower and be stronger and longer lasting then the original etc, if anything?
If your a pro you could reflow it, if not you could either look on ebay for a replacement card since its a seperate physical card luckily, or just replace the unit whichever is easier for you - the unit is getting a little old spec wise (unless you got a decent one like Core2 ~2ghz, 2+gb of ram and what not).
And btw before jumping the gun and actually blaming the video chip - make sure its not your memory or a standby isssue causing all this - if you have two sticks of ram try one at a time to narrow that down, and remove the battery and AC source power for about two minutes to narrow down the posible standby issue.