I actually had several different cards early after I got the original, including (but not everything) a Voodoo2 12MB, a TNT2Ultra, and a MatroxG400Max. Since I still play the game, it doesn't need to be said that every GF card I've had has been used with it.
I can honestly say that the video cards, while making some difference in the game (mostly in the form of color depth or minor performance boosts) contributed less to the increases in performance than upgrading my processors have (started out with a Celeron 300a @450 and now using an AthlonXP2100+ at 1845Mhz..)
Obviously the game's addictive, because it's been the main driving force for my upgrades as well as the primary benchmark I have used for determining what works best for me. I expect UT2003 will be the same in the future, now that I'm playing more of it than the original (and as soon as I see a copy of the game on store shelves, it'll be mine, mine