Yes,if you choose not to make a registry backup during installation,you could go back later and run the wizard,to make the backup from within Spybot.
You can run the wizard by opening Spybot,then click mode up top,then advanced mode.On the left,click Settings->then settings.In the main window on the right,click Wizard,to bring up the Wizard you saw when you first installed Spybot,and you should see the option to backup the registry.As you know,if you skipped backing up the registry when you installed,to skip the next options,just click next.
To return Spybot from Advanced Mode,click mode up top,then Default Mode.
To see where the .reg backups are located,please read this-
http://forums.spybot.info/showpost.p...49&postcount=2
*note-If you can't find some folders in the path,they are most likely hidden by default by Windows,so you'd have to unhide hidden files and folders.