A short while ago someone else was querying much the same issue.
I'm not sure where that thread resides, but my reply was roughly this:
If you cannot trust a person with the access allowed with a guest account, then you should bar that person from your computer completely ... and if any unpleasantness happens, then better now than after the damage has been done.
The other questioner wanted to be nice to others in his hostel, but I suggested that it ain't always wise to be nice.
Is there any way of Restricting by Xp guest login from using My computer or Windows Explorer.