You’d think iTunes 9 would have a menu option to convert selected, non-DRM’d files to .MP3, .AAC and such. It doesn’t, but there’s a quick–if not silly–workaround to get iTunes to covert your tracks to a supported format.
Mac instruction for iTunes v9
Open Preferences -> General -> Import Settings. Change the “Import Using option to the format to which you want to convert.
Within iTunes, select the file you want converted.
Under the “Advanced” menu, you should now see a “Create XYX Version”. Click it and your selected file(s) will be converted in the background while retainer your originals.
Remember to change your import preference settings back to normal!