You can do this by clicking start | run and keying scanregw.exe and clicking OK.
This will check your registry and offer to back it up.
Click Yes.

You can restore the registry by restarting your computer in MS DOS mode and keying
scanreg.exe /restore
and press ENTER.
Select the most recent backup and follow the on screen instructions.
Note: The backup you created will be flagged as not being used to start windows.  This is normal for manual backups.