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.