OK. I'll be honest.
tl;dr - and I only skimmed Nihil's post about installing keyloggers.

Just something for everyone to keep in mind, check your local laws before installing any type of keylogger, either software or hardware. In MANY jurisdictions keyloggers are per se illegal under wiretap statutes because they actively intercept wire communications.

If you're going to pull the ol' "This is MY box" route, you may need to notify every user that their usage is recorded. Thus giving them the opportunity to either consent (use the computer) or not consent (don't use it.)