Welcome to CB. You can't play iTunes files on your Pearl. iTunes uses DRM to protect their files from being played on other devices.
Not every music file of his has to be protected. Open itunes, plug your blackberry up and set it to be used as a mass storage device. Click what you want and drag it into the folder you want your music.
Blackberrys can't handle DRM protected music but you should be able to find some programs that will convert AAC formats to MP3 or other playable formats easily. I use a freeware program called iTunes Sync which syncs selected playlists in iTunes with my Pearl. Works well.
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