AMD users always are behind Intel in terms of updating their systems. Day after official release of 10.5.3 by Apple, Intel users could update easily with Kalyway or JaS combo updaters. But lately even updates for AMD are as easy as updating original Mac. All you have to do is download Zephyroth`s update tool from his site. When you run OSX86 on your machine you should have it already installed but when not you can find it here (direct download - 4.4mb)
Zephyroth`s guide works with 10.5.1, 10.5.2 and 10.5.3.