on the machine you wish to access yours from go through the start menu
start > programs > accessories > communications > remote desktop connection
then simply tap in your IP (should be static with adsl) and user/pass then change any options you want and click connect
Port 3389 needs to be available
BUT i've always used it without a firewall ... my friend uses Zonealarm and cannot get it to work with it even after allowing port 3389 ... Maybe you'll have better luck...