it uses a PCI Express BUS interface (which is new) and your machine only supports AGP 2X/4X
with a new motherboard, it would be possible, but with a proprietary dell case, i'm not sure how easy it would be to put a new mobo in, and really if you're talking about replacing the motherboard, that prolly means the processor, and you've said you want a new video card, and you're gonna need more than 256MB ram... well hell, you've almost got a whole new computer right there.
sorry bout the busted link,
try this. That 120GB Seatgate with the 5 year warranty looks like a good deal to me, but you've got lots of options.
and damn this thread for making me realize how NOT up to date my box is
