Can Tight VNC be used to connect from a broadband link to a dail up link?

I configured TightVNC on my MOTHER's computer about 50 miles away.  I set the login password for it, enabled the VNC Server service so it runs at boot time..  I had my MOM connect to her dail-up Internet Service and while she was connected, she emailed me the wide area address that was allocated to her for that session (she is not BEHIND a router or firewall).  While she remained connected, I used Tight VNC to attempt a Remote Desktop connection with her computer and could not get through... Could not connect at all..  TightVNC didn't install any Windows Firewall options and I did not see an optional box to check to allow VNC to pass through.. Should I create a port in Windows Firewall?  I don't want to disable the firewall for troubleshooting because then the computer will be infected with worms almost immediately..   As I said, she doesn't have a hard ware firewall sitting between her computer and the Internet..

All I can think of is that the VNC Server service was not running when I tried to connect.  Maybe next time start the session manually, instead of using the service?  I don't knoware you sure you're using the right IP adress?
have her go to ipchicken.com to FIND out

also, try realVNC, I managed to set up a (local) connection between my mac and my pc with THATIF you're using it to help her while she's on the computer you could also use Crossloop.  Requires that she give you an access number but it's based on tightVNC and is easy to set up and use.For others who want to know what this is about:
http://www.youtube.com/watch?v=7PEbeIHODs4