It just depends on how fussy the card or motherboard is. My 4800 is supposed to need a 4x slot to work, AFAIK, and therefore won't work in my Viglen (British PC mfr) P3/450. It works, but it won't load the drivers under XP, it only uses the built in VgaSave driver (despite the fact that it loads the drivers and works fine under Ubuntu 7.10) However, it will work just perfectly in a Dell Dimension XPS R400 (upgraded to a P3/1 Ghz) which uses the exact same Intel 440BX chipset and has the same 2X AGP slot. Go figure.