How to backup registry?

Windows Vista

• Click the Start --> All Programs > Accessories > Run.
• In the Run dialog box, type 'regedit'
• Click OK.
• In the User Account Control window, click Continue.
• On the File menu, click Export.
• In the File name box, type a file name (sample.reg)
• select a location where you want to save the Registry Entries.
• Click Save.

Windows XP

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

Note If System Restore is turned off, an instruction will appear 'whether to turn on System Restore now'. Click Yes. Then, in the System Properties dialog box, click to clear the Turn off System Restore check box, click OK, and then repeat this step.