255.255.255.255?
Not wrong. The IP addresses assigned to the VPN are endpoint addresses and as such not part of any network. The connection is point to point, not point to net or net to net.
You can achive what with routing. In order for routing to work, network addresses on both sides of the network need to be different. For example, if you are using 192.168.1.0 on the server side, you could not use the same on the client side.
Though not technically correct, Microsoft VPN clients will help you a bit. If you assign the VPN connection addresses that fall within the server side network (even though due to the mask they do not "belong" to the network), the client will add a route to the server side network when the connection comes up. The subnet mask for the route is assumed based upon the RFCs, so if you are using a 10.x.x network with a 255.255.255.0 mask, you may not be able to access all of the network.
Hope that helps.