Don't you hate it when you forget to log in before you post ... anyways, that's mine above. By the way, this link has a great description of the problem.

If you don' t believe my reasoning above, think about this: What if there were 100 doors, you picked one, Mr Hall reveals 98. This means you were either right the first time (1% chance) or you should swap (99% chance). To check this out, just change the $Doors to 100 above.