Now that iTunes songs are DRM-free, you will most likely want to convert downloaded songs to a more user-friendly format (namely MP3) for use in ANY media player.
For the PC, go to the EDIT menu, then PREFERENCES. Halfway down the first screen, you should see a button for "IMPORT SETTINGS:"
Once you click "IMPORT SETTINGS," use the drop-down menus to change the default from AAC to MP3. I also change the quality to 192k so the songs sound better:
Click "OK," then "OK" again, and now, when you right-click a song in your library, you'll see the option to "Create MP3 Version." Awesome!