oh yeah, i get those all the time!!! does it make UT shut down and then a big box shows up with a bunch of symbols and words. i think it's probably because of the crack, cuz i have the cracked/warez version of UT.
i'm pretty sure that it wouldn't be the video card cuz glide (which the voodoo's support) are the most stable for the games that support it. also, i only got the general protection fault once with my voodoo2's on my old computer but i get the fault alot (maybe once every couple times i play)on my new computer. which is running Direct 3D on a GTS2.
what kind of processor are you using?
actually, it would be a good idea to list your's and your brother's total system specs. that could help us determine your problem a little easier.