In OS X 10.5.8 Leopard this option is not there unless you have an iPhone or iPod Touch. In OS X 10.6 Snow Leopard it's there regardless of the situation. I think it will be worth it to spend $29 to get Snow Leopard.
However, there is a hack that will allow you to enable the feature in 10.5.8. It involves editing a .plist file.

http://lifehacker.com/393855/enable-google-contac...