We'll have a couple of laptops sitting at a table at a convention we're going to soon. We're not concerned about physical theft - the laptops will be physically secured, and there'll be someone keeping an eye on them most of the time. There's also no sensitive information on them.
However, we want to make it as hard as reasonably possible for someone malicious to go in and format the hard drive, or delete everything from the Windows folder, or install KILLALLNERDS.EXE from a USB drive while the minder is distracted. Alternatively, if someone does manage to ruin one, we'd like to be able to get it back up and running ASAP, without spending 3 hours reinstalling windows and all the software.
The laptops are running fully up to date Windows 7 (I think 64-bit edition), and will be physically networked to a printer, but not connected to the internet.
What's the cheapest way to reasonably do this? Protecting this from some master hacker isn't important - all we care about is making it hard for a bored kid to do some damage.