The Windows XP guest account is not only used to allow guests to login to Windows XP but also to authenticate the computer in peer to peer networks. Disabling the XP guest account is therefor only advised if you do not use file sharing, printer sharing or Internet connection sharing. Please note that file sharing refers to the build in Windows XP functionality and not applications like Bittorrent or Emule.
Disabling the account in the User Accounts menu of the Control Panel does not disable it but simply removes the icon from the login screen. Users who connect to the computer in Peer to Peer networks still authenticate as guests.
To fully disable the Windows XP guest account you need to use the following command in the command line. Open the command line by pressing Windows R, entering cmd and return afterwards.
Use the command net user guest /active:no to disable the guest account with the consequences outlined above. Windows XP Pro users can alternatively disable the guest account in Computer Management. Navigate to Local users and groups in Computer Management and click on the Users menu.
The right pane displays all current user accounts. Right-click the guest account and select Properties from the menu. Check Account is disabled to fully disable the account.