Personally I would go with the AMD 64. I would aim at getting a Opteron based version. Maybe with just a single processor to start with then when funds allow stick in a second.

I haven't seen any reviews where people have used Maya, they all seem to use Max or lightwave, but performance is very good with these apps running in 32bit mode so I would assume Maya should get similar results.

A friend of mine is running a amd64 3200 with xp64 beta and that seems fairly stable but I couldn't say for sure how it would run with a beast like Maya, it may get a bit flakey.

If not the AMD64 I would go for the P4, I'm loathed to say it being a firm AMD supporter but they do seem better than a XP in terms of performance in apps like Maya, but you do play alot more for P4 systems over AMD XP(32).

So in sumation AMD64 is as fast, if not faster than, P4's at same speed in 32bit work. When 64bit finally comes of age then you will get a further performance gain. In my opinion if your spending a sizable amount of cash you want to protect you investment as much as possible and this seem to me to be the best way.

Hope this helps Kurt.