Open Regedit. Navigate to :
Hkey_Current_User\Software\Microsoft\Internet Explorer\Main
Check if these keys exist in right hand pane : RunOnceComplete and RunOnceHasShown .. Set their value to 1. If they dont exist, create these keys.
In IE8 I noticed, the runonce keys are preceded by IE8 so the keys to change are IE8TourShown, IE8RunOncePerInstallCompleted, IE8RunOnceLastShown .. These keys should be set to 1.