Probably have to convert them to another format like Mp3, and it can be done within ITunes.
further Steve's response, most iTunes music has very strict copy and usage protection and it will throw up an error code when you try to use it in a video editing project.
Converting it to mp3 may help -- but converting it to WAV is even better. Although you can simplifying the process by buying any music you plan to use in your videos from Amazon, which has much more lenient copy and usage restrictions built into their music.
(In other words, blame Apple, not Adobe.)
Supplemental information on a way to convert iTunes music to wav version that should work in Premiere Elements
Any questions, please do not hesitate to ask.