Though more expensive, Intel processor systems work better. But for gaming you
really need a good graphics card to do well.
64 bit is good too, with at least 8gig of ram to go with it. I usually like 2 hard drives
in a system. That way you can do a quck back up to the other. Of course it's always
better to have a backup that's seperate too.. Now days USB memory sticks hold
many gigs, and don't cost a lot. So they work pretty good for a backup too.
Don't skimp on the processor and case cooling. Gaming keeps a system busy and hot.