Moving this discussion to the Photoshop General Discussion forum.
If you have the 64-bit version of either of these OSes, then:
Windows 7 and Vista (32 bit): Program Files (x86)/Adobe/Adobe Photoshop CS6/Plug-ins folder
If you have the 32-bit OS version, then: Program Files/Adobe/Adobe Photoshop CS6/Plug-ins folder
The Lighting Styles folder just needs to be in the same directory as the LightingEffects plug-in.
Secondarily, why are you wanting to use the legacy plug-in? Is it because you don't a video card that can enable OpenGL drawing?