i'm guessing that player 1 will have the blue portal gun, and player 2 will have the orange portal gun. so each one can only fire a different end of the portal.
hence the co-op
i think that will be awesome
"Money doesn't exist in the 24th century, the acquisition of wealth is no longer the driving force in our lives. We work to better ourselves and the rest of humanity." - Jean-Luc Picard