I hate looking for solutions so heres one for you.

Installed XP Pro on clean drive, and put on the latest NVIDIA drivers. Problem was still getting really horrible graphic card performance. I couldn't figure it out...THERE IT WAS. The answer to my dreams....not doubled, not tripled, but quadrupled my speed. I have a Geforce 2 MX400 64MB, not much against all the Geforce 4 Ti'ers out there but its the bang-for-the-buck deal. So I turned on all the registry tweaks. (under HKLM\Software\NVIDIA Corp.\Global\System) Total of 6 entry's put them all to (1). FORGET THE GEFORCE TWEAK UTIL. It doesnt work after 29.60 or so, the latest from NVIDIA is 30.82 for XP. It does what I just said anyway. Also THIS IS THE BIGGIE. AGP VxD Drivers. Whatever your motherboard be, get the latest and correct one. This is the big difference. WinXP has the set it thinks is right, but its beyond a failure. Go to your motherboard manufaculter and get the latest AGP VxD Drivers. Under Display Adapters/Advanced/Geforce...These are my setups

Enable buffer region extensions (ON)
Allow dual plane extensions to use local video memory (ON)
Use fast linear-mipmap-linear filtering (ON)

Depth Color for textures (Desktop depth)
Buffer-flipping mode (Auto)
Vertical Sync (Off Always)
Ansiotropic Filtering (Enabled)

Enable FOG Table Emulation (ON)
Mipmap Detail Level (Blend) Whatever your Preference

NOW if you are going to OVERCLOCK, check out this site

Great way of determining if OVERCLOCKING is the best for your card. Follow the instructions and do tests just like they reccommend. Draw out a chart and do Memory Clock first and determine highest stability point and then same for Core Clock.
REMEMBER, review methods of proper cooling so you dont kill your card.

Finally I would have to say drivers is the key, dont mess with ****ty moded drivers from wack sites, go strait to your card maker.
Dont rely on Windows XP Drivers even though its all so conviently done for you.

This is a good site for testing (basic) your system.
Here when I was having problems I was getting 50MP/s and after these fumbling to the solution now 181MB/s.

More complex solution get 3DMark2001, right of the website
Use Test one only, so you dont have to wait all day.

Good luck, if it works for you reply and say Thanks
Remember, Thought is powerful thing.

Cheers :D