From my self experiments I discovered below keys that control the Navigation Pane Per User in Open and Save As Dialog boxes on Windows server 2008 and Windows 7.
To Disable Navigation Pane:
[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\CIDOpen\Modules\GlobalSettings\Sizer]
"PageSpaceControlSizer"=hex:00,00,00,00,00,00,00,00,00,00,00
[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\CIDSave\Modules\GlobalSettings\Sizer]
"PageSpaceControlSizer"=hex:00,00,00,00,00,00,00,00,00,00,00,00
[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Modules\GlobalSettings\Sizer]
"PageSpaceControlSizer"=hex:d0,00,00,00,00,00,00,00,00,00,00,00
To Enable Navigation Pane: