Hi, I'm a Maya user myself (the guy that Seventh-Monkey referred to), so let me see if I can help out.
Firstly, if you're gonna be running any 3D package you'll need at least a Gig of RAM, off the bat. 512 won't cut it. Heck, a gig barely cuts it (that's what I use, and rendering is unstable to say the least, and it's also slower due to the lack of RAM). RAM is extremely important for doing 3D graphics, more so to some extent than your 3D card.
I'd recommend getting as much ram as you can afford. 2 Gig is good, 4 Gig is ideal.
Something that is often misunderstood by people who run 3D applications is where the graphics card is used. It's not really used for the rendering (unless you purchase a specialist 3D card aimed at Maya/Max users) all that much, but is infact used for displaying the viewports within the application. You need a decent graphics card in order to keep your feedback in the viewports at optimum. The less powerful your card, the quicker your viewports can become bogged down. There's nothing more frustrating than having to wait five minutes to rotate your viewport because your card can't cope with the poly count. It slows you right up, which is bad for productivity. I use a Radeon 9800XT and, for what I do, it copes fairly well. However, I'd recommend getting perhaps the 2nd latest generation of card (due to the fact that the prices are always a lot cheaper than the latest iteration of cards, and the performance difference isn't too great). I've heard a lot of speculation that nVidia cards are better for 3D than ATI. Whilst I use an ATI card without problems, it could well be true that an nVidia card would offer me even more performance. It's something I need to look into because I'm going to be building a new 3D workstation rig this summer, as high spec as I can afford, ready for when I go to university to take a 3D-Animation degree.
However, rendering is another key issue with 3D. Noone in 3D likes rendering, it's always the downside, an uphill battle between quality/detail and render times. When rendering, 2 elements are vital. RAM (as previously stated) and your CPU. It is infact the CPU that will be the main factor that effects render times. It's the CPU that's the raw power producing those frames. A dual core CPU (or dual CPUs) are ideal for 3D. Maya will eat up all that extra power with pleasure (though I think you might need to config maya to use all available processors at render time, because I'm not sure if it sees dual cores as seperate processors or not). The amount of RAM you have basically effects how much data you can have in your scene when you go to render out. If you have too many polys, for example, and you don't have enough RAM then Maya will probably crash on you part way through the render. Which is never good. And, if you are lacking RAM, then you'll end up having to use virtual RAM, which will cause a major slow down with rendering.
Yes, your graphics card will have some play in rendering. I'm not sure exactly how much, but definately some. I think that Maya will draw on the processing power of the card for rendering, but the main use of the card, like I say, is for the real time viewport display.
To recap:
512Mb of ram WILL NOT CUT IT!
1 Gig of ram BARELY cuts it.
2 Gig is good. 4 Gig is better
Graphics cards aren't as important as you might think. Put money towards the RAM and CPU before the graphics card.
The CPU is important. Dual core or Dual CPUs are a definate bonus.
You might want to head over to www.3dbuzz.com and have a search through the threads there. It's a 3D focused community, of which I've been a member for a good few years (lookout for 'stevetwist', that's me ;)). There are always threads of this nature popping up, and there are a lot of people who know their stuff.
Hope this helps out. If it does then you should thank Seventh for contacting me
Steve