LogMeIn may be a more practical solution than Microsoft’s Remote Desktop.
It is easier to use and endorsed by many support centers.
Install on your machine and your friend installs the client.
Routers and firewalls also present unique challenges for Remote Desktop Connections. In many instances ports have to be forwarded if such devices/software exists on the machines in question.
Portforward.com has a comprehensive list of ports, related devices and software applications.
The LogMeIn software trancends most required configurations and eliminate such challagnes.