Apple has published its "Introduction to Universal Binary Programming Guidelines".
The extensive document is available for download from Apple's Developer Connection, and aims to help developers understand how to modify and build applications to run as universal binaries.
Universal binaries are Apple's internally-developed solutions designed to help developers make applications that run on PowerPC and its new Intel-based architecture.
Apple explains the document: "Describes the prerequisites for building code as a universal binary and shows how to do so using Xcode. It also discusses the differences between the Intel and PowerPC architectures that can affect code behaviour and provides guidelines for ensuring that your universal binary code builds correctly."
The guide includes sections on Apple's home-made emulation layer, Rosetta and x86 equivalent instructions for AltiVec instructions. It also features a detailed account of the architectural differences between PowerPC and Intel chips.
Apple warns that the information in the document is not final.