Booking System Plugin

I was wondering if anyone knows of a plugin or hack that will allow the use of WordPress as a booking system.

Working in a school we have number of computer suites that available to staff to book for their classes and we would like to make the booking online. Departments already have WordPress websites and therefore a bolt on to that site with a plugin would be great.

It just needs ‘slots’ or lessons that could be booked by a user and then that session is made ‘not available’ for others to book.

Anyone any ideas, would be much appreciated. Thanks,