Disable Laptop After Set Date or Time Period

Hi

I'm trying to manage a pool of Windows 7 loan laptops that are intended for our users to borrow short term. We are having a hard time persuading people to bring them back, which means we never have any available when people need them.

So, I would like to try and find a way to loan out a machine for say 30 days, and somehow disable the computer after that amount of time.

Users do log in using their AD credentials so I don't want to disable their accounts because they will still need to log in to their desktop PCs at the office.

I can't see any built-in way of doing this, is anybody aware of any third party software that could do this for us? One thing I did think of is to write a script that runs on startup, checks the date and runs a shutdown command if a certain date is exceeded - would this potentially work and if so could anyone help with the script???

Of course any other ideas would be appreciated.

Thanks