Windows 7 WIndows Guest account to auto delete everything on logoff

There's no option like that. Files stay even if the Guest account is turned off after being used for some time. The only way to do it is to create the standard user (set some parental controls for better protection) and after using, delete the account. It will delete the files too. But that's just stupid :D

Try some software like that Deep Freeze. It suppose to be very good at that what you ask for. But there are complains about it too (it can screw your system a bit). So either, use this stupid method or try the risky one. :D