Move to another hardware platform.

What's the easiest way to move a system from one hardware platform to another? I have a fully functional system that runs on a motherboard with Intel P4 CPU, and I want to move it to a motherboard with a AMD Athlon CPU.. Peripherals like network adapter and graphics adapter is identical. I guess that I can't just lift out the hard drives and move them over and then expect the system to work? Anders Norrbring