We can make changes in the registry that can enhace our windows OS by increasing speed or changing visually etc. You can find lots of Windows Regisrty Tweaks here in Trap17 and also in number of other sites.
But It is very very Important to make a backup copy of the registry before you go to apply the twek by making changes in the registry. By this you can reset your registry back if anything goes wrong.
Here is the steps to be followed to make a backup of the registry.
Step 1: Select Start Menu >> Run, the Run dialog box will open
Step 2: In the run dialog box type regedit and click Ok
The Registry editor window will open.
Step 3: In the left pane of the Registry Editor select the My Computer, which is the Top most node in the Tree.
Step 4: Right Click on My Computer and Select Export. The Save as dialog box will open.
Step 5: Give a name for the registry backup file preferabbly the date of saving in the File Name Text Box and Select Registration Files (*.reg) from the File Types List.
Step 6: This is the most important Step save the registration backup file in a partion other than that in which the OS is Installed and select Save.
Now you've made a backup of your registry. You can fearlesly modify the keys in the regisry and try the new tweaks.
Now lets see how to reset the registry with the backup file that we've created in case any thing goes wrong in the regisry or in the system. The steps to be followed are,
Step 1: Select Start Menu >> Run, the Run dialog box will open
Step 2: In the run dialog box type regedit and click Ok
The Registry editor window will open.
Step 3: Goto File Menu and select Import from the menu in the registry Editor.
Step 4: The Open File Dialog Box will appear, navigate to the location where you've saved the backup of your registry and seclt the file and click Open.
Now you've done it, your registry has been reset and restart the system after resetting the Registry to make it work properly.

