I have used PPTP VPN from Windows 2k on several machines. You must have the cypher strength (internet explorer help window) at 128. Use high encryption pack for win2k if not at 128bit. Every win2k machine I have vpn'd with was at service pack 2.
Windows95, that is a headache, but I got it to work. You need the 128bit DUN 1.4 update that microsoft has removed from their site. Email me direct if you want this file. Note that this only works with 95. 98 and 98se have their own 128bit DUN 1.4 installs, which I have those as well. Making IE 128bit cypher in Win95/98/98SE does not make the default DUN PPP connect at 128bit. I don't know if these can be uninstalled, so you should research this before putting on an important system.