The information are stored in the registry using a simple ROT-13 encryption. Windows XP saves the full path and name of the program, last access and the number of total executions. UserAssist is a nice little tool that decrypts the information and displays them it its main window. You can clear single entries by right-clicking and selecting clear. If you do have many entries in that list you might want to clear them all by clicking on commands, clear them all.

This does not disable the logging, it simply clears the current state. Windows XP will continue to log all activity unless you disable the whole process by clicking on commands, logging disabled. This will take effect once you restart, logoff and on again or kill the explorer.exe task in the task manager.

The manual way to disable logging would be to open your registry and navigate to the key

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\UserAssist\Settings\NoLog

and set the value of that key to 1.

Windows stores the encrypted information in the key

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\UserAssist

Please note that you should not disable or clear the feature if you want to work with the recent items in your start menu.