PC that must work with Maya, Adobe and Games

First of all if your budget allows it, I would try and create different computers for your gaming and production activities. Maybe just upgrade your current PC and use that solely for gaming, then buy a new one just for graphics production.

As for Maya, I've run it pretty smoothly on my old computer so any modern processor (around 3ghz) would be good. Of course if you are concerned with rendering times then look into top of the line dual (triple,quad,etc...) core processors

Pixar uses 2.8ghz Intel Xeon processors (1024 of them) in their renderfarm; which also features two terabytes of memory and 60 terabytes of disk space.

As for Adobe products, if you are fine using CS3, any processor as far back as maybe five years will probably give you satisfactory-exceptional performance. If you are running CS4 though you will probably want to have the most up-to-date computer possible. The only really CPU hungry products I've noticed by Adobe in my experience are After Effects and Premier, so again if you plan on using any of those for post-production you will probably want a top of the line processor/motherboard combo and plenty of ram to spare (no less than 2 gigs).

As for graphics cards, my old computer had an ATI card and my new one has a NVIDIA card and I didn't really notice any difference between the two in Maya. If you have been hearing bad things about ATI though and you believe the claims are credible then go with NVIDIA. I would try to get a card specially designed for graphics editing though as the demands will be slightly different than for your typical gaming card and you will most likely have better performance and rendering times with a professional card. Nvidia's Quadro line and ATI's FirePro cards may be worth looking into.

Of course try to get a motherboard that allows for the most ram possible (I hate rendering...) and use a operating system that supports that amount of ram. A 64-bit OS and at least 6 gigs of ram would probably be your best bet. I would also try and get a hard drive with perhaps a little less storage but a really fast data access rate, possibly a solid state hard drive if you can afford one, to use solely as a scratch disk as this will improve your performance greatly in Adobe's products.

In the end though despite what me or anyone else says just go with what ever you can afford. It is all too easy to come up with this perfect dream system that ends up costing well into the tens of thousands of dollars, but if your budget is only $500 dollars set your expectations accordingly. I would try looking at Tiger Direct and possibly consider getting a bare-bone system (w/o OS). They have pretty nice deals on those every once in a while, and I think I got a good deal on my last PC I purchased there. I would also continue browsing around on computer graphics forums and see what types of rigs other people are using. Not many members here would probably be able to give you the best advice in that sense.

Jam it back in, in the dark.