Why is everyone complaining about the 425 watt power supply???
You will not need a new one for an 8800gtx!!
I have a 375 watt dell psu with my xps410 and I am running an 8800gt.
My 375 watt has dual 18V rails. Please check the sticker on the side of the psu before bitching about it being crappy.
BTW most dell bioses are crippled. There are no options for overclocking, adjusting memory timings, and such.