While that's good advice if you're making one or two changes in the Windows XP registry, it's not practical if you're making many changes or are concerned about making accidental changes to the registry.
In the method described below, you backup the complete Windows XP registry, giving you the opportunity to undo any problem you might cause when making edits.
Note: The steps below require working with the Windows Registry in Windows XP. Making changes other than the ones described below could cause serious problems in Windows XP.
Execute regedit to start the Registry Editor program.
See How To Open Registry Editor if you need more details on that.
On the left pane of Registry Editor, locate Computer, which will be all the way at the top.
Click once on Computer to highlight it.
Choose File from the Registry Editor menu and then choose Export....
Once the Export Registry File window appears, choose a location to save the registry backup file to.
Note: You want to be able to easily find this file if you need to restore the registry backup so be sure to choose someplace easy to get to, like the Desktop.
Enter a name for the registry backup file in the File name: text field.
Note: Name the backup file something logical like XP Registry Backup DATE, substituting the current date for DATE. Anything will work, just keep it simple so you're not digging around for it if you need it later.
Confirm all the above choices by clicking the Save button.
A file named with the name you just chose, with a REG file extension, will now be saved in the location you specified.
At this point you can start making changes to the Windows XP Registry.
If for whatever reason you need to undo the changes you've made, you can use the backup file you just created to restore the Windows XP registry, returning all keys and values to back to the way they existed when you made the backup file.