New
#11
If you just want them to not be able to use the computer, just remove the power cord and bring it along with you. Hell, remove the monitor cable.
If they're going to go so far as to removing the HDD to mount it elsewhere to get at the stuff on it, you may need to reassess those "friendships".
Maybe you can make it a raid 0 system, and simply pop out and carry one of the drives with you?
Use software restriction policy ... very easy to setup and locks it tight.
I see then I'm going to have to use some kind pad lock or something and TrueCrypt on the computer thanks people.