The user interface in Inventor 2010, 2011 and 2012 can be switched between the default ribbon and the old classic environment with tool panels.
The UI switch can be found in versions 2010 and 2011 in the dialog "Application options": Tools > Application options > Colors - the "UI Style" options - Ribbon and Classic.
This option is missing in version 2012 but you can do the same switch by modifying a Registry key. In:
change the key InterfaceStyle to 1 (classic interface) or back to 0 (the default, ribbon). The practical usage of this switch is rather limited in version 2012 as it does not anymore contain predefined commands in the individual tool panels (they display as empty in the default view).