elemnar and I used to spend ages playing this when we were small. As with so many games, we invented our own two-player version of it as well. I think I moved the player and elemnar gunged the enemies? That's often how we ended up turning single-player games into co-op ones.
We kept doing that even into the Wii era - with the Wiimote/nunchuck setup each person can have half of the controller. One of the better games for this was the shootouts in Rayman Raving Rabbids, as the wiimote did point/fire and the nunchuck did grab/reload. Usually it was a race to see which one of us would splat a rabbid first!