If your Photoshop CS5 Installation does not find your TWAIN Scanner it is because some plugins are not included in Photoshop anymore. To be able to scan pictures from within Photoshop again do the following:

1. Download the plugin pack which includes the TWAIN plugin from Adobe: http://www.adobe.com/support/downloads/detail.jsp?ftpID=4688

2. Put the files from "\PSCS5OptionalPlugins_Win_en_US\Optional Plug-Ins\Win32\" to "c:\Program Files\Common Files\Adobe\Plug-Ins\CS5\" and restart Photoshop, you should be able to find your Scanner in menu "File - Import"