I don't think nowadays you have to worry too much about the system. Computers have become powerful enough that any new basic system will run maya for modeling, and animation. Unless you're really picky about Render time which does make a big difference on the system you use. Sometimes you want to pump out your work at the fastest time possible.
Believe it or not I have a IBM T40 laptop I bought on '04 for 300 bucks.
Processor is 1.6GHz
Mem 768 mb of ram.
ATI radeon 9000 with 32mb of memory.
I have this because I model and animate only on my laptop sometimes when I'm on the go. When I'm at work I transfer all my files from the laptop and render everything on our farm. So I don't mind. I'm cheap! lol
For you I would recommend:
* At least have a minimum of 1 gig of Ram.
* An Nvidia Quadro video card with 128mb (nowadays any video card works properly with maya like ATI, but NVIDIA is the best of the best)
* A 1.8 gig processor.
These are the most important things to have. You can even get a basic dell that will work very nice with maya. Don't try to invest too much on a computer. Technology is always advancing and they depreciate with time. Just get something basic for the meantime.
A great site for some sweet deals if you want to build your own: