Well you'll need a graphics card, but it isn't really required for botting, since it relies more on your processor/ram, a GT 430 or 440 would be more than enough.
I really don't know how much RAM you'll require since some bots use more than others, and the amount you run in the same client would require you another amount of RAM.
You can always add more RAM if you want, but if you do; try to use the same model, otherwise it isn't guaranteed to work.
Same for cores, I think a i5 would do. I don't know about AMD.
Note that Intel released Sandy Bridge a few months ago, and AMD is planning to release Bulldozer procs soon.