Unfortunately, you need 10.5.8 minimally. Leopard is no longer in production. It is obsolete. You do not have an Intel Mac so Leopard is as far as you can go with OS X.
To find Leopard go to eBay.com, Amazon.com, or search through Google. The links go to pages where Leopard is being sold. Be sure to buy only a true retail full installer disc. They will have a box cover like this:
The disc will also appear the same.
You need to upgrade the computer's OS to 10.5 or newer. If you're using a PowerPC Mac as you seem to be, purchase a Mac OS X 10.5 DVD from a source such as Amazon or eBay, run Software Update, click here, and install the software.
Whatever version of Leopard you purchase, I suggest updating it to 10.5.8 which should have everything you require. To update Leopard download and install Mac OS X 10.5.8 Combo Update. Alternatively, open Software Update and install all the recommended updates. That will include the above updater.
To update your phone:
4. iPad Support
a. Updating Your iOS to Version 6.0.x from iOS 5
Tap Settings > General > Software Update
If an update is available there will be an active Update button. If you are current,
then you will see a gray screen with a message saying your are up to date.
b. If you are still using iOS 4 — Updating your device to iOS 5 or later.
c. Resolving update problems