Since you can't undelete users without a full system restore, here are alternatives to consider: • Change users' password to prevent access to their account (is your Guest Account also turned off?) • Change the user account type from admin to standard, to limit what they can do (explained below).
To delete an account, type "user" in the start menu's search box and click "User Accounts":
Click on "Manage another account" when the Control Panel opens.
Select the Windows account you want to delete:
To remove administrative privileges from a user instead of deleting the account, click on "Change the account type", pick "Standard" on the next screen, and click OK.
Otherwise, click on "Delete the account" for the final confirmation screen:
To keep the user's data, click "Keep Files". Windows 7 will create a folder, named after the user, with their content: Documents, Favorites, Music, Pictures, and Videos. It won't keep data stored in their AppData folder, for example. (Note: Outlook 2010 saves PST files inside Documents).
To completely erase that user's profile and data, click "Delete Files" instead.