Another user account is created for the ASP. Net Worker Process (Aspnet_wp.exe) so that it is not running with administrator privileges. This helps to increase security because if there was a breach the worker process is running as a lowly restricted user rather than having administrator privileges on the local machine. The big complaint with there being another user account is that when it is created, it will prevent auto logon had there previously only been one user on the computer.
This information was found here:
http://www.mvps.org/marksxp/WindowsXP/aspdot.phpIt says it is for XP, but the information still seems relevent except for the part that tells you to download and run the registry file. That obviously won't work cause you can't log in.
If this doesn't work, then there is a password reset CD you can get that works really well. It's not Ophcrack. I have never had any success with that. I will look for the CD when I get home. I forget what it's called.