Require password for Guest Account

I am setting up five mac minis in a coffee shop for public use. The Leopard feature of Guest Account w/ Parental Settings is exactly what I need. Limited application access w/ removal of the sessions data upon logout. The one draw back is the lack of a required password to log into the computers.

Is there a way to require a password for the Guest Account or should I look at scripts to remove and reset the account to a default with a standard account?

Any help or direction is greatly appreciated.

Why exactly does the account need a password if it's for public use?

There should be an easy way to reset account data on logout for a regular account, Google around.

The computers are public use, but a charged service. The owner wants to make sure that the customer requests, places id before logging on, and then is charged based on the time used.

I am currently looking around for a good option, but I have not found one yet. Any help is good help.

There are some programs that restore everything to how it was every time the computer reboots. Have a look here:

Faronics Deep Freeze Mac - ABSOLUTE Workstation Integrity

Seems like a solid solution, but probably more than is needed for just a coffee shop. I believe that there is a solution without using third party software. Thanks for the direction!