|When you have the viper installed, does anything ever show on the screen? If so, go into cmos/bios setup to see if you need to change the primary video adapter to agp. If nothing shows on the screen, how did you attempt the driver install you mentioned in # 3?|
When using the viper, if you get a posting screen or gateway logo when you first boot up, try going into safe mode with the F8 boot menu. If you get to safe mode uninstall the ATI drivers. Then reboot to normal mode and see if it picks up the card.
There are some compatibility issues with AGP cards. Not all AGP cards work in all AGP slots. This is a download for the manual:
Check the card's specs and see if it's compatible with your agp slot.
Since you apparently haven't booted into windows using the viper it's possible XP will have native support for the card and will install its own drivers--if you get windows to load with the card.