That's where programs such as Windows Remote Desktop Sharing, and LogMeIn's LogMeIn Pro2 can help out. LogMeIn's new join.me service also fits the bill.
In this video we show you how to:
Remotely log into and control someone's desktop using Windows Remote Desktop SharingRemotely log into and control someone's desktop using LogMeIn Pro2
Note that LogMeIn Pro2 costs $70, but the free version allows you to share desktops for the first two months or first two hours of use. Logmein join.me is free.