In all cases, when working in the Registry, the user should back-up a full copy of Registry, prior to making any necessary changes.
Fortunately, ERUNT is a utility that is compatible with all versions of windows.

Making a System Restore Point, is also recommended, but not sufficient when working in the Registry.
Windows native Registry Backup does not, provide a full restorable copy of Registry, and that is why ERUNT is recommended.

http://www.larshederer.homepage.t-online.de/erunt/

For an excellent overview and instruction of How to use ERUNT, see Ztruker's article:
http://forums.whatthetech.com/index.php?showtopic=99376