windows2000

Actually, you don't have to have *any* other OS to install 2000...unless you mean get an upgrade license. Per Microsoft, you can upgrade to 2000 professional from 98 (and even 95) as long as your system meets the hardware requirements. To Upgrade to2000 server, you need to have a 3.51 or 4.0 NT server.

http://www.microsoft.com/windows2000/professional/howtobuy/upgrading/path/win9x.asp

Hope this helps!