Step One: To show the On My Computer folders in the navigation pane, click on Outlook in the upper left hand corner on the toolbar menu, then click Preferences.
Step Two: Under the Personal Settings section, click General
Step Three: Next, under the Folder list (the only list), clear the check mark on Hide On My Computer folders check box.
Further information and help can be found at:
http://office.microsoft.com/en-us/mac-outlook-help/about-on-my-computer-folders-HA102928232.aspx