Here's another scenario in further clarification....
I installed PS CS5 to my K: Drive (rather than to the C: Drive).
When the PP Studio V10 PS Plugin installer ran, it did not see PS CS5.1. I had to use the Manual option. I pointed the installer to the K:\Adobe\Adobe Photoshop CS5.1\Plugin sub directory. The Installer completed without advising of any error nor inadequacy.
Rebooted the system. Launched PS CS5.1. It showed no sign of Anthropics nor PP Studio V10 under the Filter pulldown menu, nor, under the Help > About Plug In.
With PS running I launched PP Studio v10 and re-ran the installer. This time it did automatically see PS CS5.1. I allowed the Installer to proceed. PSFilterPPLauncher.8bf was placed into the C:\Program Files\Adobe\Adobe Photoshop CS5\Plug-Ins subdirectory.
Relaunched PS CS5.1 and there was still no sign of Anthropics nor PP Studio V10 under the Filter pulldown menu, nor, under the Help > About Plug In.
In order for PS CS5.1 to properly show Anthropics > PP Studio v10 under the Filter pulldown menu and Portrait Professional to appear in Help > About Plug In, PSFilterPPLauncher.8bf had to be placed into the K:\Adobe\Adobe Photoshop CS5.1\Plug-ins directory!
Also note that the PSFilterPPLauncher.8bf file is the only file in the root of that subdirectory. It is not contained in any Anthropics nor Portrait Professional directory within K:\Adobe\Adobe Photoshop CS5.1\Plug-ins! This is not the convention for all the other plugins. They are contained in a product or company named subdirectory below, the K:\Adobe\Adobe Photoshop CS5.1\Plug-ins subdirectory.
I installed PS CS5 to my K: Drive (rather than to the C: Drive).
When the PP Studio V10 PS Plugin installer ran, it did not see PS CS5.1. I had to use the Manual option. I pointed the installer to the K:\Adobe\Adobe Photoshop CS5.1\Plugin sub directory. The Installer completed without advising of any error nor inadequacy.
Rebooted the system. Launched PS CS5.1. It showed no sign of Anthropics nor PP Studio V10 under the Filter pulldown menu, nor, under the Help > About Plug In.
With PS running I launched PP Studio v10 and re-ran the installer. This time it did automatically see PS CS5.1. I allowed the Installer to proceed. PSFilterPPLauncher.8bf was placed into the C:\Program Files\Adobe\Adobe Photoshop CS5\Plug-Ins subdirectory.
Relaunched PS CS5.1 and there was still no sign of Anthropics nor PP Studio V10 under the Filter pulldown menu, nor, under the Help > About Plug In.
In order for PS CS5.1 to properly show Anthropics > PP Studio v10 under the Filter pulldown menu and Portrait Professional to appear in Help > About Plug In, PSFilterPPLauncher.8bf had to be placed into the K:\Adobe\Adobe Photoshop CS5.1\Plug-ins directory!
Also note that the PSFilterPPLauncher.8bf file is the only file in the root of that subdirectory. It is not contained in any Anthropics nor Portrait Professional directory within K:\Adobe\Adobe Photoshop CS5.1\Plug-ins! This is not the convention for all the other plugins. They are contained in a product or company named subdirectory below, the K:\Adobe\Adobe Photoshop CS5.1\Plug-ins subdirectory.