Q: How can I recover my play counts and ratings?

iTunes: How to move [or copy] your music to a new computer [or another drive] - http://support.apple.com/kb/HT4527

Quick answer if you use iTunes default preferences settings:  Copy the entire iTunes folder (and in doing so all its subfolders and files) intact to the other drive.  Start iTunes with the option (shift on Windows) key held down and guide it to the new location of the library.

The above is how you should do it.  Your playcounts and ratings are stored along with all other information about your iTunes collection in the library.itl file.  If this wasn't part of the move then they got left behind.

What are the iTunes library files? - http://support.apple.com/kb/HT1660

More on iTunes library files and what they do - http://en.wikipedia.org/wiki/ITunes#Media_management

What are all those iTunes files? - http://www.macworld.com/article/139974/2009/04/itunes_files.html

Maybe iTunes just turned off the sidebar. Press command-j to show the viewing options, and then select "play count" and "rating".

Hope it helps.