AFAIK, there's no setting for that in Win7. See if Classic Shell can help.

>With Windows 7, when we click on a folder in Explorer, it refreshes the right pane with the directory layout. However, unless we click on the little arrow on the left, the directory in the pane we are clicking in will not expand. We have to double click on the folder to have it expand. I searched for a setting so to have it like XP Pro but was not able to find it. If someone knows where such a setting is, that would be appreciated.