If you are sceptical or just dont want to mess with the registry you can do this through the graphical interface.
Single-Click or Double-Click to Open an Item Step 1
Navigate to the Control panel usualy located under
START>CONTROL PANEL Step 2
Once in the control panel change the drop down menu in the top right corner to
"Small Options"
Step 3
Now find the icon that is named "
Folder Options" and point and click
Step 4
Once in the folder options window under the
General tab find the box that is labeled
Click Items as Follows. In this box is an option that says
Double Click to Open an Item (single click to select) To the left of this is a circle be sure to click this circle and choose
Apply then
OK