Offline NT Password & Registry Editor to the rescue!
I did a dumb thing on my workstation: I disjoined it from the domain and joined a workgroup; an irreversible change that left me stranded without a way to log back in after rebooting. Fortunately, there is a great tool/utility called the Offline NT Password & Registry Editor.
There is an executable on our machines that joins the machine to the network, without the need for an administrator to log in and perform the steps manually. I knew that if I could just run that, everything would be fine. Unfortunately, getting in was not at all possible.
The Offline NT Password & Registry Editor however, proved very handy. What you do is to make a bootable CD/diskette, which allows you to change the passwords of any local users (and give them admin priveleges as well) on an 2000/XP and up installation. It’s really easy to use, so much so that you can pretty much press Enter at all the prompts.
That way, I was able to log in, run the join domain executable, and cancel the call I had logged with the help desk, before anyone had contacted me back, and before I would perhaps had to give an account as to how this situation came about.