By stating you have the problem with NT and XP boxes...does this mean that you don't have the problem with other o/s's or these are just the ones involved?
Technically, if you have one static IP and you set up a VPN on it, you will have to use that VPN connection to be able to access the network and then use VNC once you are inside. Unless you can route the VNC requests through the VPN or router to go somewhere else...which I think may be difficult. I don't know of another way without getting an additional ip address.
Have you tried looking at the documentation for Real VNC on their website? I know it has a section on routing through firewalls, there may be some information there that is helpful with the VPN software.
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"It's become appallingly clear that our technology has surpassed our humanity." --Albert Einstein
