I was able to download and install iTunes 10.6.3 onto my iBook G4 1.33GHz 1.5Gb RAM and running OS X 10.5.8. It also works just fine for the most part with of course some limitations.
It was available in Software Update and installed normally.
http://s1078.beta.photobucket.com/user/RedCroissant/media/iBookG4_zps8410c116.png.html?sort=3&o=0
It was available in Software Update and installed normally.
http://s1078.beta.photobucket.com/user/RedCroissant/media/iBookG4_zps8410c116.png.html?sort=3&o=0