Still have Quake lying around? Try this graphics mod for it -
http://tenebrae.sourceforge.net/downloads/TenebraeInstall.exe
After that, get this optimization to greatly improve your FPS - http://www.modeemi.fi/~jpaana/tenebrae_full_sse.zip
By the way, you'll have a little trouble with water in the game. All you have to do is set r_novis to 1 in the console.
http://facelift.quakedev.com/retexture/ - A big retexturing pack. Goes in Quake/Tenebrae/Override
http://tenebrae.sourceforge.net/downloads/TenebraeInstall.exe
After that, get this optimization to greatly improve your FPS - http://www.modeemi.fi/~jpaana/tenebrae_full_sse.zip
By the way, you'll have a little trouble with water in the game. All you have to do is set r_novis to 1 in the console.
http://facelift.quakedev.com/retexture/ - A big retexturing pack. Goes in Quake/Tenebrae/Override