hope you have a card reader on your computer. put sd card in computer and drag and drop mp3's from your itunes library to your sd card. don;t know if your car will play music encoded as .AAC or .m4a (Apple codecs)
Itunes isn't my favorite resource, but I do have it and am somewhat familiar with it.
Itunes does have the ability to convert an AAC file to an MP3 file -- sometimes. In Itunes highlight the song you're interested in, right click it, and select "Create MP3 version." This will only work for songs that are available in an unprotected version, and there may be a minor charge to "upgrade" from the DRM version to the non-DRM version.
But, if recent news reports are to be believed, Itunes will be shifting over to non-DRM songs in the near future.
If you don't have a card reader in your computer you can get a device that looks like a fat flash drive. You can put the SD card in the "fat drive" and plug it into a USB port. That's the way I do it.
Edited by Capn Easy, 14 January 2009 - 09:53 PM.