Originally posted here by x acidreign x
download a tool called ntpasswd, it is a bootdisk utility that can reset windows 2000 and xp passwords. after you've logged back into your machine, run msconfig and select the startup tab to select which programs and services you want initiated at startup, if there's a keylogger on your system, chances are it's here. run antivirus, windows update, then read a tutorial from the tutorial section about how to secure your box against intruders (there are plenty, pick one). the bad news is: in the hands of an experienced hacker, no box is secure when you're sitting in front of it.. the good news is, this guy sounds like anything but. If your systemadmin or boss won't fire this *******, take that ntpasswd disk over to his box, see how much skill this guy actually has. chances are if they wouldn't fire him, you're fine too.
Personally I would not do this at all, since you put yourself at risk of disciplinary action.

Speak to your sysadmin about the problem you are having with your machine and ask for it to be fixed.

Speak to your HR department about your coworker and explain what you beleive has happened and ask for advice. Mention that you beleive your supervisor may be involed

If you think you know why they are doing this, tell that to you HR department.

Don't do anything whatsoever to your PC - Let the IT dept fix it.