The Windows XP trick worked for me:...
I tried this and it worked. However I was logged on as a Power User and was running Regedit as the very Administrator account I wanted to hide at the login screen when I was making the registry edits. Once I closed the program I couldn't log into anything as the Administrator from the login screen or the Run As Administrator menu.
Luckily "runas.exe" from the command prompt still let me run regedit as the Administrator so I could delete the new registry keys and get back to square one.
Is there any way to make the default Administrator account hidden on the login screen but still avaiable for the Run As option in the GUI?
Also, I looked, and my Administrator account isn't a member of Users, so taking it out of that group is apparently impossible.
(edit)Oops, I just realized that I resurrected this topic. I just followed the link from one of the comments on the main page and didn't think to check the dates. Sorry.