In Windows XP, rename the user name folder that's located in "c:\document and settings\user name folder", will do the trick, but He is the proper way to do this in windows 7 To delete a user's profile, do the following:
1) Backup the files under that profiles before you delete it. Favorites,documents, etc.

1) Control Panel, System and Security, Advanced, and click on settings; select the user profile you want to delete.
If the user name is grayed out, please do a complete shutdown and turn on the machine and the user profile will unlock and you will be able to delete it.