CNC control electronics questions

I'm getting closer to my dream of a home CNC. I just purchased a
power supply off eBay. it's a 24V, 40A power supply. will it be
sufficient size?

Also, I'm still trying to clarify exactly what I need. I think I've
narrowed it down to this:
(3) 600 oz. in. servo motors from dan mauch
(3) Gecko G320's
(1) "Magic Box" - see this picture
http://web.umr.edu/~bpryor/pics/cnc.gif
(I still need the stuff that's outlined in red in the picture)

I'm unsure as to exactly what goes into this "magic box," but I think
I need something to connect the drivers, power supply, and computer.
Am I correct? What is in this box? Can I build this, or do I need
to buy it pre-assembled?

Also, I still need CAM and CNC software. I already have AutoCAD R14.