Nvidia 8800 GTS?

I have a Dell XPS GEN 5 Specs: 3.4 GHZ P4 HT, 1 GB DDR2 RAM, 250GB HD,Double Layer DVD Burner, DVD Drive, Front Bay media card reader, Sound Blaster Audigy 2 ZS, nvidia 256mb 6800 GTOC, power supply 460 watts, I was looking into getting a nvidia 8800 gts 640mb or the 320mb, since Dell has its own parts and what not which we all know is hard to upgrade anything major on it, my question is will this pc be able to handle the video card, im also going to be getting 3gb ddr2 ram, please respectful opinions thanks again