"This is an area for regular users with a minimum of 28 days as a member and minimum 250 posts (excluding classifieds). If you would like to use this board you need to apply through the 'Regulars' user group (found in your control panel)"
a co-op is where one of the moderators arranges a group/ bulk buy of nappies or similar usually from US - to save on postage/ get extra discounts for bulk buying
It encourages people to become part of the comunity here. As co-ops requre a certain level of trust for payments etc it helps to protect the mods who organise the co-ops. It is suprisingly easy to get to 250 posts if you are a bit of a chatterbox like me