Shoutbox

Like I said, I have used Deep Freeze Unfreezer many times and I've never had a problem, so IMO, it should be safe to use it.

DFU is very straight forward: Just launch it, click detect status, select boot thawed, click save status and reboot your computer. To enable deep freeze again just repeat the steps but this time choose boot frozen instead of boot thawed. It's that simple.
If you're not an administrator, then you will have to launch DFU via the task scheduler which allows you to run an application as an administrator. That requires the task scheduler service to be enabled.

However, if you do mess your school's laptop I won't be responsible!