Prevent Guest from editing XP Registry

How do I prevent the Guest account from being able to edit the Registry? I'm running XP Pro on a non-networked system.

I don't want to use the DisableRegistryTools key in the Registry, because that would lock me out if I ever wanted to undo the change. I've tried GPEDIT, but that doesn't seem to allow the setting of permissions for one specific user account (unless I'm missing something there). Using the Edit | Permissions menu in the Registry doesn't seem too useful either, as that menu is also accessible to the Guest, who can just re-set permissions if s/he's knowledgeable. (And anyway, the permissions I set in that way from my own administrative logon (Read vs. Full Control) don't get reflected in the Guest logon.)

Short of 3rd party software, how do I do this? Thanks for any help.

 

IMHO, that is a rude guest. I have "used" computers in libraries, public rooms, etc etc and never had the urge to enter the Registry. Break his/her fingers??
Seriously, I can't find a way and I know this is Pro, right? There is 3rd party software that will do it, among other things you may or maynot want envoked. I am wondering if TweakUI, or something along that line, which is free will do the job?