I recently installed Snow Leopard. It works faster than before and it gave me 8GB of space back. But, after looking through Applications in system profiler, I found out iTunes is not 64-bit unlike Safari and other native applications that have been re-written to 64-bit. I remember Apple said iTunes is also re-written. I must download a new version or it's included in an update (I'm waiting the 10.6.2 update to download at the moment)? Is this in the wrong forum (there's an iTunes forum)?
iTunes is still 32-bit because (as far as I know) it's still at least partly written in Carbon. To my knowledge there's no 64-bit iTunes version.
No, that is due to iTunes' codebase sucking in general, due to it being written originally for an OS it no longer even supports, and having feature after feature after feature tacked on to it.
Perhaps in iTunes X (iTunes 10) it would be 64-bit based. Or maybe earlier... What would that be? Mac OS X 10.4 and below?
No. Mac OS X "Panther" 10.3 and earlier, though I think the intent was even earlier than that... iTunes 1 was originally designed for Mac OS 9
Probably not, but it might still contain design decisions and constraints from its early days. Overall structure, having to be backwards compatible with old file formats, etc... Don't know for sure though. Only an iTunes engineer could really tell you that.