I would go with Intel on this, IMO if you are doing any sort of CPU intensive programs besides games or multitasking a lot, which you normally do with programs like CAD, photoshop, etc.. I would say get a P4, but if you plan on doing gaming the A64s are a better purchase
Hmm... Well yeah I guess Opteron would be a good choice, I was thinking about cheaper parts like the na 64s, and the northwood/prescott P4s. But a Dual Opteron rig I think would be the best if you have that much $ to spend.