Silicon,
If the server on the remote side is a W2K DC and also acting as a DHCP server, it will assign an IP address to the client VPN machine automatically depending on how you have RAS configured. And when you VPN from the client, even though the private ip is say 192.168.1.23, the remote VPN server sees the public IP assigned by the client ISP. And when you configure the client you tell it to use the public ip of the server ISP. So I'm confused as to why you couldn't have the same private ip in use on each end.