I thought I would check back in and put some peoples minds at ease. I have been playing for over a week now with my dell XPS 410 and 375 watt dell PSU + 9800gt with absolutely no problems.
Its a pny geforce 9800 gt 1 gb card BTW
I have been playing fallout 3 in "ultra" setting at my monitors max 1280 X 1024, smooth as glass. I am amazed how much better this game looks on ultra versus my old medium settings.
Left 4 dead with max settings at that resolution is also perfect. This is not a system killing game anyway and ran pretty well on my 7900 gs. But I can turn on AA etc without a thought now.
The ATV racing game "Pure", which my 7900gs would barely run at low, runs perfect at max settings as well.
While I dont have any of the latest system killing games, every single game I have (graw2, rainbow six vegas, hl2, CSS, TDU,DiRT,Race 07, and more) runs perfect without any slowdown or hiccup. I will be getting crysis this weekend and will let you know how things work out.
If you need a band aid to get a little more time out of your old XPS I recommend this card. You can find the 512 mb cards for around $90 at compusa, $95 at newegg.