with less than a geforce 2 they just slow down the game unacceptably. with a geforece 2 or better - turn em on and enjoy the show. theyre good. very good.
if you have some weird card post what it is and someonell tell you if its good enough or not. and in any case almost any card can be made to run opengl to some degree, go to
www.glsetup.com and run the web setup. at worst itll leave your card with the same performance, and it could be well worth it.
oh, and you cant be limited to 32bit colour, cos thats more than the maximum the human eye can distinguish (and dont let any console boy tell you different, a 128 bit console still runs in 24 bit colour, although the processor is different). in fact, no gaming PC yet built has more than 32 bit (in terms of colour or cpu)