back up the registry in in Windows XP

Source :- Microsoft

Manual steps to back up the registry in in Windows XP

1. Click Start, click Run, type %SystemRoot%\system32\restore\rstrui.exe, and then click OK.
2. On the Welcome to System Restore page, click Create a restore point, and then click Next .
3. On the Create a Restore Point page, type a name for the restore point and then click Create
4. After the restore point has been created, click Close.

Use System Restore to undo registry changes in in Windows XP

1. Click Start, click Run, type %SystemRoot%\System32\Restore\Rstrui.exe, and then click OK.
2. On the Welcome to System Restore page, click Restore my computer to an earlier time (if it is not already selected), and then click Next .
3. On the Select a Restore Point page, click the system checkpoint. In the On this list select the restore point area, click an entry that is named "Guided Help (Registry Backup)," and then click Next. If a System Restore message appears that lists configuration changes that System Restore will make, click OK.
4. On the Confirm Restore Point Selection page, click Next. System Restore restores the previous Windows XP configuration and then restarts the computer.
5. Log on to the computer. When the System Restore confirmation page appears, click OK..

Source :- Microsoft