Geez, this discussion is just too full of very mature statements.
Since Im just too stuborn to leave threads like this be, here's my take on the various OS's.
Win9x, mostly useless, horrible memory management, horrible for networking, horrible stability(blame 3'd part programs all you want, a good OS wont allow a crappy program to take the whole system down, thats what protected memory spaces is for).
Win2K, best Windows by far, makes for decent servers, and actually a good workstation.
No real weak points, all half decent hardware out there has drivers these days, compability is pretty much equal to Win9x as long as you have a decently new computer.
Very good networking support.
Linux, the best workstation if you know what you're doing IMO.
Harder to get into, but much nicer to work with once you get going, not to mention it makes a perfect server.
Hardware compability is mostly a non issue as long as you stay with known quality components, the situation is worse if you go cheap and buy el cheapo hardware.
For the avarge user, I'd go with Win2K, I dont have the patience to teach someone Linux, unless they're willing to learn, in which case they'll probabaly do fine by themselves.
Win9x is a big no-no for anyone these days IMO, unless you have a very weak computer, in which case Win95 is the way to go.
And Stalinator, try to act a bit mature will ya?