yeah, CS5 is kind of goofy for scanning.
You have to go to Adobe and D/L something called
"PSCS5_OptionalPlugins_Win32"(assuming your OS is 32-bit) and extract a
file called "Twain_32.8BA" from the folder OptionalPlugins/Win_32.
Copy/Paste this file into the Program Files/Adobe/Plugins/Import-Export
folder.
Now you are good to go to scan from the Photoshop File menu using your
installed scanner.
HTH
Gary W. Chmura