Hi you can just get rid off any other accounts in Control panel, User Accounts. You can turn the Guest account off or on here also.
It seems strange you have another Admin account. Anyway look in there and see if it helps.
Sorry if you have already tried this..
If you really need a replacement for TweakUI...Microsoft are not releasing a replacement but suggest you might like to try this.
http://unlockforus.*************/200...tures-gap.html