Note -- Most games do work on new OSes. I have hundreds of PC games, and of the Windows ones, only a very few actually don't work on my newer, Windows Vista 32-bit PC. It's a bare handful of a large number of titles. Use compatibility mode, the other options, DOSBox... that'll get most stuff working. But there are those few stubborn games that I'm unable to get working, and for those there's DOSBox...
Which games have I been unable to get to work? Hmm... Scorched Planet works, but not correctly. Pitfall: The Mayan Adventure works, but you can only play in a window, fullscreen crashes it. Heavy Gear 2's speed is messed up so mech legs look like they're moving at hyperspeed, even while they actually aren't moving any faster than they should (maybe slower, actually?). A few games don't work at all, including Q-Bert (Hasbro's remake), Front Page Sports: Ski Racing, and Metal Gear Solid 2 Substance. There are a couple more I have which don't work, but I forget them offhand. But really, it's surprising how many do work even on Vista.
(Oh, anyone with 64-bit Windows will have a much greater need for an older PC, because any Windows 3.1 or before game will not work, and even many later games use 16-bit installers, making it impossible to install the games, even though if they were installed they'd work. 32-bit doesn't have that problem, so compatibility is much better.)
Yottamol said:
:lol
(...thinking back...Windows ME was my only OS for six years...)
Same here, WinME was my only OS for 5 1/2 years, and that old machine, over nine years old now, still works. Yeah, it crashes a lot, but it still works, and it'll play most of those games that DOSBox and Vista can't (Windows titles incompatible with XP/Vista/7, mostly, DOSBox does a good job with most DOS games; there are some that don't really work and require an older machine, though).
I'd say Win 98 SE is the better OS, but ME does work. Oh, I never cared much about the removal of easy access to real DOS mode because, first, you can use a boot disk to get to it if you want, and second, my WinME computer has a Soundblaster Live! soundcard, and with Creative's Win98 drivers installed, it's got great emulated DOS Soundblaster 16, MIDI, etc. support. (The card came with the computer, and came with two CDs of drivers, one for WinMe and one for Win98; the default ME drivers had no DOS Soundblaster support, which was pretty frustrating, until I tried installing the Win98 drivers over the ME ones. That fixed the problem, DOS emulation added.

)
Oh, and while it does crash or slow down and need a reboot a lot, as I said, that WinME machine still works, and has never had a major hardware failure, needed a reformat, or anything since I got it in late 2001. Still running on the original installation. ME's really not as bad as it's claimed. It's not great, sure, and they did some pretty stupid things with it (why was DOS mode hidden, why does System Restore not really work (I know, System Restore works fine in XP, Vista, etc, but ME... not so much), why is it less stable and crash more, etc, but they added some things too, and if you know what you're doing it'll work well enough.
Of course another option is just getting an SB16 or AWE32 or what have you.
Oh yeah, and a 3DFX card of some kind (as an addon card of course) is probably worth it... a lot of late '90s games really benefit from it, and there's nothing quite like the real thing. Even on newer machines, with the various 3DFX driver emulators that are out there, they won't work with every game like the real card will, and those emulators are unlikely to work well on an older machine anyway. I'm not sure which is the best Voodoo card though, Voodoo2 or Voodoo3?