I upgraded my iphone to V6.0.1, now itunes cannot see it when plugged in. i can't upgrade itunes because it says it has the latest version. i can't upgrade my OS X V10.5.8 because it says it is the latest version. what do i do?

I upgraded my iphone to V6.0.1, now itunes cannot see it when plug it into my macbook. i can't upgrade itunes on my mac because it says it has the latest version 10.6.1(7). i can't upgrade my operating system,OS X V10.5.8, because it says it is the latest version. what do i do? I assume i need to purchase an upgrade for my operating system to then upgrade iTunes? What version do I need to upgrade my mac to and is this something i can do all online?