I’m pretty sure that WinXP doesn’t ship with an OpenGL driver for your Voodoo3 (since 3dfx is out of business). You can try http://www.voodoofiles.com or http://www.x3dfx.com to find a driver for XP.
Good, I think you will enjoy the new video card much more.
Just be sure you fully uninstall all the drivers for the voodoo3 before installing the Geforce, and you should be fine! Also make sure you download the newest drivers from Nvidia.com, as the ones that come with the card on the CD are never up to date.