None. The maximum OS for a G4 or G5 Mac is 10.5.8, and syncing devices running iOS 7 requires at least 10.6.8.
Actually, Getmessi's profile says his (or her, sorry) iPhone is running iOS 6.1.3. If this is indeed the case, this iPhone can be synched with iTunes 10.6.3, which is available at http://support.apple.com/kb/dl1575.
Just don't upgrade to iOS7!
Well, if you could score a first edition MacBook 13" with Intel-based 1.83GHz coreduo or later, you would have no trouble using the fairly good and stable Snow Leopard 10.6.x from the retail installer DVD.
Then update that to the last steps available as downloads from Apple via the software update. And hope you don't need to get the App Store in order to do that. At least you'd be on a supported side of hardware, not PPC.
However the early editions of intel-based Macs also
have upgrade limitations, as the path goes forward...
If that version of iTunes works with the older iPhone iOS, that's a fair idea.
Good luck & happy computing!