Obviously the faster the cpu you get the better performance but i would suggest at least a dual core since Maya is at last multi threaded, i personally have a quad core .
Make sure your case has very good ventilation since rendering and simulation make the cpu run at 100% and overheating can be an issue if you are not well ventilated.

You can get by on 4 gigs of Ram but ideally at least 6 or 8 would be preferable or more if you can afford it if you plan to do animation.

As for Graphics card ..Maya will run on budget cards and gaming cards but you really need a workstation card with open GL with at least 512MB onboard ram but better with 1GB or more .In my experience Nvidia cards have less issues and tend to run smoother i suggest the best QuadroFX card you can afford.

Lastly to take advantage of more than 4 gigs of RAM you will need a 64bit OS so either XP64 or windows 7 64bit.