chntpw, CHange NT PassWord, can be used to modify Windows registry files offline and change windows passwords.
It could also be used to modify the startup programs to stop viruses from starting.
To install from a live instance, you will need the other apt repo's uncommenting in sources.list and then you can simply
$ sudo apt-get install chntpw
For reference, the majority of Windows 7 and Vista registry hives are in these two locations