By default, iTunes only allows song ratings in full-star increments (e.g., ). However, the program has the capability to display half-star ratings as well (e.g., ), but the setting to do this is hidden.
You can enable the assignment of half-star ratings by editing the user preferences file. To do this, first close iTunes. Then, with a text editor open C:\Users\UserName\AppData\Roaming\Apple Computer\iTunes\iTunesPrefs.xml on Windows Vista/7/8 (or C:\Documents and Settings\UserName\Application Data\Apple Computer\iTunes\iTunesPrefs.xml on Windows XP). After the following lines:
<key>User Preferences</key> <dict> </dict>
add the code:
<key>allow-half-stars</key> <string> true </string>
When you restart iTunes, you will be able to set half-star ratings in addition to the full-star ratings in the iTunes Library window by clicking and dragging the area in the ‘Rating’ column of a particular song.
However, changing the rating by right-clicking the iTunes icon in the system tray will still only allow you to assign full-star ratings. The ratings menu is also nested one level deep, and therefore takes a bit longer to access. Since I often use the tray icon to rate songs rather than switching back to the library window, I have developed a free software tool called iTSongRater which adds an improved iTunes navigation and rating icon in your system tray. When the iTSongRater tray icon is right-clicked, the pop up menu allows you to directly assign full and half-star ratings right from the start, and also allows other features such as changing the playcounts of songs. Try it out! It is much more useful than the default iTunes tray icon.
Tested on iTunes 10, 11 & 12.2
Edit, April 9, 2022
It seems that the above method no longer applies to the most recent version of iTunes (12.12). Instead, start a command prompt (Start menu, type “cmd”), then run:
"C:\Program Files\iTunes\iTunes.exe" /setPrefInt allow-half-stars 1