http://www.newegg.com/Product/Produc...-315-_-Product is the video card i use for 4-5 Boxing, lately i have been 5 boxing due to the prices of keys through Blizzard.

I'm running a AMD Athlon II X4 640, 3ghz
4GB DDR3 1600 RAM
Standard 7200 RPM drive(nothing fancy at all)
Dual monitors, Isboxer window layouts. Main window at "fair" settings unless i'm in a big crowded area(City, etc) other windows set to far left of the graphics adjustment bar.
Along with that video card i just linked above, I can manage 12 - 15 fps constantly(/console maxfps 15), unless i rush a Galv turtle in AV or something along those lines.

All in all, if you're on a dead line budget and don't mind 12 - 15 FPS, I can suggest that card, Which is what i use, and i run almost always on 15 FPS.