Before you make any changes in your Windows Registry where you're not completely sure of what you are doing, it might be a good idea to make a backup of your current registry settings. You can either do that by creating a System Restore Point or do a backup of only the registry itself. To do the latter, enter it by typing regedit into a Run... prompt. Right-click on Computer on the left frame (the root directory of the keys) and select Export:
Choose a directory where to save the backup and hit Save. The file that is created that way is a *.reg file and can be merged (in this case it replaces the whole registry) on double-click.
This way you create a backup of the whole registry. It is a good idea to have a full working registry backed up, but you can also back-up smaller parts by exporting sub-keys of Computer.