Well, this is kind of funny because the PSP does support the AAC format. You can't use iTunes to transfer the music, but with a USB cable you can transfer the music yourself.
PSP media managers will make it easier to copy the files, but most of them will convert the files to MP3 which is unnecessary and could affect the quality of the song.
If you want to copy the music to the PSP yourself, copy the music to the \PSP\MUSIC directory on your PSP. If the directories don't exist you can create them, but make sure to use all capitol letters when creating the direcories. Once the music is on your PSP, rename the file extension on each song file from .M4A to .MP4. Once you do this, the songs should appear on the PSP and be playable...
Hope this helps...
Z.
Fast enough... Windows XP Pro