You might run into DRM issues, depending on how old the tunes are and also format issues if they are not MP3 files (I've not tried AA files on my Eris).
Barring all of that, you could simply connect the phone to your computer, go to the iTunes files in "My Music" (or wherever the raw files live) and drag them from the folder to the phone's SD card folder.
When I have my SD card opened from my Droid on my PC, I click and drag the songs from iTunes to the music folder and it works just fine for me.
That works for me too. I just open up iTunes & drag each song I want into the music folder.
Does it even play the ones you download from iTunes? Like the DRM music?
I have downloaded the whole Lady Gaga Fame Monster Album, the Bad Romance Music video, and copied the whole album and the music video just fine to my SD card. Everything plays just fine.
Cool. I wonder if the older music will. That is pretty awesome. I wonder if it would work on my wife's blackberry. She uses itunes I don't. I was never cool enough for an iPod I always had generic MP3 players if I had anything at all. The bright side for me is I would be able to use all her music. LOL.