Password Reset

I have an operational Dell Workstation which I have forgotten which is the password for the windows login. I have tried to use a number of password reset utilities such as Winternals ERD Commander to reset the password. When Winternals boots from the CD Rom it does not find an OS image for some reason. Is there something I can do in regards to the Winternals issue? Or is there another way around the Windows Password without having to rebuild the PC? Is there another utility out there that I can use to reset the password? Any advice would be greatly appreciated.