Okay geeks, I need your help.

Here is the deal:
My mom wants me to have remote access to her computer so I don't have to drive 2 hours every time she has a problem. I thought while I was at it I'd set it up on my sisters computer (same router) too.

I set it up using RealVNC for remote connections and dnydns.com to broadcast the IP address of the router.

The problem is I can make it work with 1 computer (1 server & 1 dns account) but with 2 computers acting as VNC servers listening on different ports, broadcasting IP on 2 different DNS accounts it won't work for either of them.

Is there any way I can get both computers to accept VNC remote connections?

P.S. All machines are running XP