I agree that Gentoo will probably work, as it still has functional i486 support. Be aware that you may be spending a lot of time compiling if you go that route and don’t have a second, faster machine to use for distcc or the like.
As for the nvidia card, the proprietary driver won’t work for something of that age. Check the supported cards in Nouveau (and maybe even the really old drivers for prehistoric cards). In a pinch, the vesa driver should work. Good luck.