Don't restrict yourself to ancient parts just because you plan on using an older OS. After hunting down this stuff (most are discontinued models, if not all), it's questionable weather it'll even last.
The last PC I had that ran these older games (and still have it running around here) is a P3 500, Abit BE-6, Crucial PC-133, an Asus GF2mx200 (the Voodoo3 2000PCI it replaced was just as good IMO) and the first line of the Creative SB Live! Platinum cards (has a daughter card and not a live-drive) that still emulated older SB cards. An alternate to this board that may be more available is the Asus P3B. They're both slot1, which may be available at a nice price.
And they are dirt cheap on eBay!
Perhaps the most important part may be the soundcard. If it's games like dukenukem3d or redneck rampage, a Soundblaster32 PCI
would be a safe bet as far as compatability goes.