What is the default administrator password?
The correct password is Evaluation1. Just look in the readme file
You haven't put any work into modifying the system, so just start over. You'll probably spend more time trying to find a password solution than just reinstalling the OS.
As an aside, I suggest making a copy of your virtual disk after a fresh working install, so you don't have to actually install if you do want a fresh machine.
Free password recovery tools:
Windows Password recovery - Can retrieve forgotten admin and users' passwords in minutes. Safest possible option, does not write anything to hard drive.
Petter Nordahl-Hagen's Offline NT Password & Registry Editor - A great boot CD/Floppy that can reset the local administrator's password. See the FAQ for more info.
Openwall's John the Ripper - Good boot floppy with cracking capabilities.
EBCD – Emergency Boot CD - Bootable CD, intended for system recovery in the case of software or hardware faults.
But as others have said, you have nothing invested in this install -- easier to just blow it away and start over.