Ok, that last post raises questions. Half Life does not require 3d acceleration, but looks like a dog in software mode. The Geforce2 overall looking to be the better buy, but 3dfx just slaps anyone else silly in any Unreal engine based games because of the ability to run Glide.
Anyone who wants to play HL seriously will have 3D on (and OpenGL rather than D3D). In UT, the 3Dfx's can use glide as it gives them a performance boost, but in HL it doesn't really matter - Half-Life was designed using the Quake game engine so none of todays 3D cards will be pushed extra hard by it.
Half Life does not require a 3D accelerator. You could play it on a K6-2 300 with a 2 Meg ATI card if you really wanted to.
FSAA is really good on the V5, thats what I got it for. Since Half Life is more CPU dependant, it actually looks good with good framerates with FSAA at 1024x768 on my P3 866.
Both Half-Life and Unreal Tournament have software renderers. Neither one requires a 3D accelerator to run. Both look much better when used with a 3D accelerator, but their software renderers are pretty good, all things considered.
Quake 3 Arena, as far as I know, requires an OpenGL-compliant 3D accelerator. There is no software renderer in the engine.