I cannot sync my iphone because my version of itunes is too old, but I can't upgrade my itunes because my os is too old. Software updates says there are no available updates

The requirement for the latest iTunes (ver 10.7) is an operating system of Snow Leopard (Mac OS X 10.6). You will have to purchase Snow Leopard, available at 1-800-MY-APPLE for $19.99. You will not be able to get it using the Software Update utility. It is also not available as downloadable content like Lion and Mountain Lion. You can check stores like Best Buy and Wal-Mart, I know it is NOT available at Apple Retail Stores. Hope this helps.