I personally (aside from the historc dimmension of "collaborateur")
would use both collaboration and cooperation for slightly different
aspects of one another. To me, cooperation sounds a bit more like the
"organizational framework", the aggreement, the cell in which people
then actually work together, collaborate. I also would say that people
come together not only to "co-laborate", to work, but also just to be
sociable,, maybe say communicate (even though collaboration normally
always also involves communication) - but i don't quite know if the term
"co-operation" still would apply to that.
Just my $.02.
cheers,
gabriel.