Windows 7 includes a nearly-hidden feature called PC Safeguard that is primarily aimed at shared consumer PCs that need to be returned to their original running state after being used by a child or guest. The feature can be enabled on individual user accounts; when user logs off or the PC reboots, those accounts are wiped clean and returned to their original configuration.
Configuring PC Safeguard: open Control Panel, User Accounts and Family Safety, then User Accounts. (Shortcut: Open Start Menu, click logon picture in the top right.) Then, click on Manage another account. From the list, select the account for which you'd like to add PC Safeguard. Or, if you don't have an account for this purpose, create one first.
Secret: 1) You cannot use PC Safeguard with an Administrator account. It can only be used with Standard user accounts. 2) To enable PC Safeguard on an account, that account must be logged out at the time. When you click a Standard user account, a new Change an Account display will appear with a list of account options. Click Set up PC Safeguard.