I want to create a private network within another. This private network (which will use seperate hardware) will not be able to access the outside network and the outside network will not be able to access the private network....BUT I want to be able to manaully allow certain IPs from the outside network to access the private network, and I want the private network to able to access these allowed IPs on the outside network. To make matters worse I can either use a Win2K box (any version) or a LinkSys Router (if it can even handle that). How can I do this? P.S. The allowed IPs range is 128.x.x.x, the inside private network 196.x.x.x.

You don't give a lot of information. When you establish a vpn tunnel, you have to specify a subnet anyway. If the IP is not part of this route, you have to add tunnels.

Most routers in there config allow for blocking. In this you would want to block all except 128.x.x.x. In so doing no traffic will be allowed to enter the router except those from the given address. My dlink also allows no outbound connections except x.x.x.x. Maybe the linksys has something similiar, check the manual.