/vr/ - Retro Games

Scored a Turtle Beach Montego II for $25, so I'm pretty happy about that.
As for best OS, I'll also support Win98SE for this purpose, but you have to keep in mind that even if you're running that OS, there isn't really a machine that's the best for such a large span of time. Your best best would probably be a Slot 1 board, so that you can use a Pentium II or III if you desire, IIIs will be better for very late 90s/early 2000s Win9x games, but even less suitable for early 90s DOS games that a Pentium II would be, plus certain cards, like the Voodoo 1, aren't really compatible with a CPU over 500mhz. If you aren't planning on playing a select few earlier Glide supporting titles, or are fine with software/early DX support for them, you don't really have to worry all that much about the Voodoo 1.
You'll also want something with an ISA slot if you're going to want to play some DOS titles, since since there's really only a select few PCI cards that have any kind of DOS support, and you'll typically run into some issues as well. If you only care about certain titles like Doom, or especially later stuff like Duke Nukem 3D, you shouldn't even need to worry about booting into DOS to tell you the truth, though.