The Registry has to be one of the least understood aspects of the Windows operating system family. A wrong entry in the Registry can potentially wreak havoc on the system.To understand the Registry is to get to the heart of controlling and modifying your Windows system. If you know what you are doing, you can turn your machine into a lean performance machine, customize and personalize its appearance, and get complete control over nearly every aspect of how Windows XP behaves.

It is always recommended that you take a backup of the Registry before proceeding with an edit, because, an improperly executed hack could cause strange behavior or even worse, could even entirely corrupt your Windows installation, requiring you to reinstall Windows. Make an Edit in the registry only if you know what you're doing - and if you do it with care.

There are two things you can do in terms of backing up the Registry:
* either back up the entire Registry, or
* export the specific key you are going to edit.

To export a Registry key follow the following steps:
01. To open the Registry Editor click on "Start" and select "Run". In the Run dialog box enter 'regedit' and hit OK.
02. Find the key or sub-key you want to edit and select it by clicking on it.
03. Choose File > Export. In the dialog box, select the location where you want to save the key, select to save it as a .reg file, and select the “Selected Branch” option. Give a name for the fileand click Save. It will be saved as a .reg file.

At any later point, you can restore the individual key you exported using the method above by a simple double-click on the .reg file you saved.

To back up the entire Registry, use the backup utility provided with XP. It is generally not recommended to export
the entire Registry or a hive using the “export” method, as any changes or accidental erasures while working with .reg file may have disastrous consequences.
* Open the backup software from All Programs > Accessories > System Tools > Backup.
* Select the checkbox that says “System State Data”.
This will back up the registry, boot files, and the COM+ class registration database.

To restore the system state follow the following steps:
* Open the Backup utility from All Programs > Accessories > System Tools > Backup
* Click on 'Advanced Mode' and select the 'Restore and Manage Media' tab.
* Select the backed up system state file you want to restore. Check the 'System State' box.
* In the “Restore Files to” box, select 'Original Location'.
* In the Tools menu, select Options, and click on 'Always replace the file on my computer', then on OK. If you don’t select this option you'll be asked for a confirmation for each and every file during the restore process.
* Click “Start Restore”. You will get a warning that says: 'Restoring System State will always overwrite current System State unless restoring to an alternative location'. Click OK to overwrite.
* Click OK in the Confirm Restore dialog box. The restore operation will start showing you the progress of the
restore.
* When it completes, click Close and accept the prompt to restart the computer.
Now your Registry will be restored to its state before you made any cahnges in it.