Problems with ARD

Hello;

Recently purchased Apple Remote Desktop to be able to access my mothers computer (I live in PHX she lives in Arkansas) and assist her as she has finally switched from PC. I sent her a disc with the client install, went through (correctly I believe) in activating ARD from the System Preferences, restarted her machine, but everytime I try to add her computer to the list using her IP address, computer name and login, I get an error message "There was a problem communicating with "xx.xxx.xxx.xxx" (x's are the IP address). We are have cox high speed internet access. We are both using panther, we both have new iMac's.

I have another computer at my home that is on my personal network with a belkin router and it works perfectly.

This is not only frustrating but embarassing.

Any help would be greatly appreciated.

thanks