Iproute
DOS program designed to run on 286+ class computers
requires another box like Linux MASQ
Microsoft Proxy
Requires Windows NT Server
Quite expensive
NAT32
Windows 95/98/NT compatible
Roughly $25 for Win9x and $47 for Win9x and WinNT
SyGate
Wingate
Does proxy
Costs roughly $30 for 2-3 IPs
Winroute
Does NAT
Lastly, do a web search on "MS Proxy Server", "Wingate", "WinProxy", or goto www.winfiles.com. And definitely DON'T tell anyone that we sent you.