More than 2 instances of Wow

[Friedpickles]

I have tried searching the forum's to no avail, maybe I'm just in overload mode. Anyways I am trying to get 5 box's 1 pc up and running and can't seem to get past the first two. I will be the first to admit that my pc is outdated however before I upgrade the pc and buy 4 more copies of wow I wanted to go the trial route first. My question is am I required to have multiple copies of wow directories/exe's? I ask because I crash on the third copy while logging into the game, I even went out and bought a updated video card hoping it was jsut my old 7800gt. I would imagine I should be able to run 5 copies of wow albeit slowly on a computer that is less than 5 years old especially since I have no slowdown at all at 2 copies.

My current specs:

Winxp Pro 32:
2.0ghz x2 processor
4gig ram
9800gtx
Rest doesnt really matter its old, built it myself.

Thank you for your time,
-Ryan

p.s. everything I've been reading leads me to believe my system is just junk for anything more than 2 boxing