5 boxing can be done a variety of ways. at one time, you would have to buy 5 machines and keyboard/mouse splitters... and go for it. then you had synergy, but you still have the same problem... 5 machines.

now you can use ahk or keyclone to enable multiple games on one machine.

here's a link to someone that is 5-boxing on a single computer:
http://www.dual-boxing.com/forums2/viewtopic.php?t=1942

my recommendation before you buy anything... spend about an hour reading the first 10 posts on the first 10 threads from the beginners haven, general, hardware and software sections. that should give you a fairly good taste of how it is done today.

if you still need more info, just let me know.

g'luck and welcome to dual-boxing