If you have a tower the best card for the money is a PNY Geforce FX5500 PCI card.
It wont kill your power supply OR your wallet.
The Dell Part Number for the Video Cards is
NVIDIA VERTO FX5500 PCI 128MB PNY VCGFX55PPB VIDEO GRAPHICS CARD (A0416878)
I have used these cards with XP SP2 and GX1, GX110, 170L, and Dimension Series without issue for SMALL MINI TOWER based systems.
Its available at Best buy, COMP USA, Walmart, etc. Very easy to find card.
Works with Farcry, World of Warcraft, Battlefield2, Doom3, HalfLife, etc.
If you install XP SP2 you dont even need to install drivers. It just works.
For Win2000 Install Directx 9.0c Redist and then install the Nvidia 56.72 WHQL drivers.