I just started Multiboxing about 3 weeks ago, I have my main on a 22" monitor and my alts on my second monitor split into 4 screens using keyclone. my system is a C2D @ 3.3 OC'd, 4 GB RAM and a 8800 GTX and i have no issues running 4 at a time. i have PIP bound to my f9, f10, f11, and f12 keys so i can switch between my alts and my main screens.