I have a Gateway with a 500 mhz Pentium III.  My operating system is Windows 98.  My current card is a 16mb #Dfx Voodoo 3 3000G. Yesterday I purchased a eVGA Geforce FX 5200 128 mb AGP  8x/4x.  After installing the card I followed the instructions and let windows try to find a driver.  It defaulted to a low setting and I tried to install the software that came with the card.  The software is suppose to remove the old drivers and install the new stuff. The software checked my system, it seemed OK,  and proceeded to start the installation wizard.  When the software attempted to modify my registry I got an error and the process stops.  I thought Norton might be the problem so I disabled and attempted again.  Still didn't work.

Note my card appears slightly different. It has two series of pins for the AGP slot.  The new card is divided into three series of pins but still fits my AGP slot.  

Any ideas?

I would start by just going to nvidia's website and downloading the latest detonator drivers. Skip the CD for now. See if that works.
[url]http://nvidia.com/content/drivers/drivers.asp[/url]

What was the error that you got?

Sounds like you had AGP 1.0 with 2 pins and now you are running a universal card with 3 pins so that shouldnt be a problem except for decreased performance.  Look in.. my computer...control panel..system...device manager... and then see if there are any yellow circles with "!" in them.  Make sure voodoo card is not showing up in there, if so remove it. Remove any reference to new video card also.  Reboot computer and when it finds new video card tell it where the drivers are.  If you know what the error says that would help a lot.