If he purchased the music from iTunes, he should be able to re-download without having to re-purchase. Using one of these third party transfer programs will definitely be faster, though.
I have a 16GB iPhone 3GS and a 2009 White Macbook running on 10.5. I recently wiped my macbook, thinking I could restore my iTunes Library from my iPhone music library. However, I cannot figure out how to do so.