I was given a VPC file which belonged to an employee who left our company. The VPC has important code and data. Anyways, I started up the instance in Microsoft Virtual PC 2007, but can't logon because we don't know any user names or passwords for the machine. How can I reset the Administrator password on the virtual machine?
The same way you would reset the passwords for a physical Windows machine. My preference is Offline NT Password and Registry Editor. It will let you change or reset any of the local passwords on the system.
Not a VPC problem so much as a Windows one... The following article from Daniel Petri will help with a lost/forgotten administrator password: http://www.petri.co.il/forgot_administrator_password.htm
I used Hirens Boot CD. The second utility on that worked fine. I found all the other utilities and boot CD's I tried to use, wouldn't work, as when they started booting into Linux there was a Kernel Panic. Now I don't know which version of the Linux Kernel they were using but I tried three different ones to no avail. Thankfully this second utility on the Hiren Boot CD does not need Linux and thus it was plain straight forward. If this worked for you - let me know.
Ophcrack is worth taking a look at. I've had plenty of luck with it and has saved me numerous times. Assuming your password isn't too obscene, it's perfect for when you want to retrieve the password, rather than change it. Can be run from a live CD.
I assume you have the vhd files and need to get to the data on it. So rather than starting the OS in it, just access the data in the file.
You could use Windows 7, which apparently supports mounting of VHDs, for now I am using a tool called WinImage, you just open the vhd file and then have read-only access to it and can copy all the data you need.
the tool can be downloaded at http://www.winimage.com