the name of software required for this is TeamViewer (freeware)
TeamViewer is a simple, fast and secure remote control application. You can use TeamViewer for the following scenarios:
Give ad-hoc remote support to colleagues, friends or customers.
Administer Windows® server and workstations (you can configure TeamViewer to run as a Windows® system service – so your computer is reachable even before you are logged in to Windows®).
Share your desktop for online-presentations or collaboration.
TeamViewer can communicate across firewall barriers and proxies without any need for special configurations!
How to connect to a partner:
. Start TeamViewer on your computer.
. Ask your partner to start TeamViewer
. Ask your partner for his ID and the session password.