3dfx to GeForce upgrade guide
Are you in for a new GeForce but not compatibility issues ? 

A lot of consumers these days are upgrading from their older model 3dfx Voodoo1/Voodoo2/Banshee or Voodoo3 based videocard for a new model NVIDIA GeForce videocard. We've are following our forums closely and noticed that a lot of those users experience problems once they have their new NVIDIA chipset based videocard installed. Examples are, DLL errors, Black screens when the game starts and a dozen other issues. Immediately the users starts to yell and think that they have bought a piece of crap videocard which is wrong. If you did not uninstall 3dfx drivers properly in the past then the chance is high that remains of libraries and registry entries are the cause of this havoc. There are two ways to solve this. The first is always the best but a bit radical, a freshly new installed Windows will do the trick perfectly of course. However, don't we all hate to reinstall windows with every system upgrade ? We do, so here's a NVIDIA to 3dfx upgrade guide to help those who are experiencing problems most common problems.

How to uninstall your old video card.
You'll need to get rid of those pesky Windows registry conflicts (sigh) from previous video cards, sometimes this is where the format comes in, but most of the time a little regediting (with the help of the board manufacturer, if necessary) will get the job done. Before regediting you could try booting in safe mode to see if any old drivers show up there. If they do, remove them and reboot. The system should detect the Voodoo3 card after that.

Using RegClean
Using Regclean to clean the registry from old 3dfx entries, Regclean will NOT clear the registry from old 3dfx entries, you will need to do this by hand using Regedit.