You can't do this in Vista (you apparently will be able to do this in
Windows 7), nor should you be using the Guest account for this. You will
need third-party software or look into using Microsoft's free SteadyState..
Create a new Standard user called something like "Visitor" for this
purpose.
http://www.microsoft.com/windowsxp/sharedaccess/default.mspx
More on SteadyState:
http://aumha.net/viewtopic.php?t=27570
SteadyState support -http://social.microsoft.com/forums/en-US/windowssteadystate/threads/
Commercial: DeepFreeze -www.faronics.com
Malke