Recently, I had to login as the local Administrator in a MS Windows 2008 server. Guess what: nobody knew the local Administrator password. This happens pretty often when a MS Windows host is part of a Windows domain because administrators usually login as the domain Administrator and rarely use the local admin user.
I found out that there are many tools to recover the local admin password, but most of them are not free or have a shareware version with a poor feature list (unless you pay, off course).
Offline NT Password Recovery & Registry Editor is an excellent password recovery tool which is 100% FLOSS and works just fine. Just download the ISO file, burn a CD or mount the ISO file in your virtual CD-ROM drive, boot from CD and follow the steps. The default options will do the job in most cases for a password recovery scenario.