2 DrewDown:
If your PC is >700Mhz - buy GF4 (i've heard something 'bout GF4Ti PCI, it's much better than that piece of sh.t called MX420 which worse than GF3)
If you have 700MHz or less and <256Mb RAM - buy Voodoo5 5500
(works ok with Jabo's plugin, and insanely fast with Glide64 and some other glide stuff (Lewpy's PSX plugin, ZiNc, Unreal/UT and it's only chance to play Undying without slowdowns)
If you have two monitors buy both cards - Excellent OpenGL and D3D from GF
and super fast Glide from V5.