I still don't understand it.
Are you building a new rig, yes/no?

Why would you put a 8800GTS into a POS Dell PC? It's going to get bottlenecked like hell and you'll wonder WTF is going on because you'll get almost no performance increase. Your mobo will probably not be a decent recent chipset and not allow appropriate RAM/CPU. I'd be surprised if it actually has a 16x PCIe slot... 250W is NOT enough to support a system with a PCIe card, so I assume that it's simply onboard or AGP or something. In 3 months the 8800GTS will be superseded by the 9900GTX (GT200) which is a completely revamped chip-architecture that is said to blow away even current dual-VGA setups. I bought a 8800GTS just recently because the price is pretty good but if you plan on actually waiting some months, I'd suggest aiming for the next generation that is just around the corner.