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:

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\CIDOpen\Modules\GlobalSettings\Sizer]

"PageSpaceControlSizer"=hex:d0,00,00,00,01,00,00,00,00,00,00,00

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\CIDSave\Modules\GlobalSettings\Sizer]

"PageSpaceControlSizer"=hex:d0,00,00,00,01,00,00,00,00,00,00,00

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Modules\GlobalSettings\Sizer]

"PageSpaceControlSizer"=hex:d0,00,00,00,01,00,00,00,00,00,00,00