Upgrade version of disc will be fine.
Can you boot into win7 at all?
If so you can try a Repair Install
Otherwise, you may have reg hives backup in Windows\System32\config\RegBack
you can copy the hives from there into Windows\System32\config.
You would need a boot disc to do that.
It can be done via the command line , which you can get to from the repair options on the install dvd.
But it is easier to use this free boot disc Rescue Kit Free Edition - CNET Download.com
Select Normal Mode > File Transfer Wizard.