I always recommend AMD. But youll be fine no matter which you choose. I would also recommend a gig of ram instead of 512. If youre really rendering on this machine, thats where more RAM really shines.
AND if you write large files to HD during exportation of large renders you may also consider a higher RPM hard disk (10,000-15,000). Thatll cut the render time nearly in half... literally. HDDs are the bottleneck of nearly every PC on the planet.
System specs? Lets just get down to it people:
My penis is bigger than yours.