Do NOT buy the FX5200 unless you really need a "BUDGET" card. It is weak having only 60% of the performance of the much older GF4 TI4200, the lowest performer of the GF4 TI series. The TI4200 can be found at similar price and is a reasonable card.
The GF4 TI4200 series are available in 64 or128 mb, 4x and 8x AGP versions. The 64 mb, 4x AGP model is as fast as the 128mb, 8x AGP one due to the ram configuration.
www.pricewatch.com starts the TI4200 at $76.
If the Dell only supports 4x AGP, then get the suitable card.
The 2 gig P4 will hold the TI4200 back a bit in FSim.
So there you have it.

Mainboard: Asus P5K-Premium, CPU=Intel E6850 @ x8x450fsb 3.6ghz, RAM: 4gb PC8500 Team Dark, Video: NV8800GT, HDD: 2x1Tb Samsung F3 RAID-0 + 1Tb F3, PSU: Antec 550 Basiq, OS: Win7x64, Display: 24&