Studio xps 8100 video card issues

I have the dell studio xps 8100 with an ati 5770 in it and I have been having problems with the card and drivers since I bought it. The display driver has stopped responding and has recovered is the error I kept getting. Updating to the latest driver package solved that issue, however in world of warcraft the game freezes for 8 to 10 seconds at a time, the screen will go gray and then it will recover. This happens every couple of minutes. I was wondering if anyone had anything like this happen to them? I was thinking the anemic power supply may be to blame, afterall ati does say that 450 watts is required and the dell only shipped with a 350 watt supply... but then I thought the engineers can't be that dumb, they must have throttled the card down to meet the power requirement.... or made some other tweaks. Anyone have any insight on what could be the problem? I am at my wits end here..... I just want to play my games. I always built my own systems and I guess i should have kept doing that..... lol I feel like buying a beefier power supply and an nvidia card.... I've had wayyyy to much trouble with the ati drivers for my taste.