How to pass the "group" ID from a node to another one??

Hey all, I would like to use prepopulate to pass OG from one node to
another. So from the first node there would be a link to add a related
node and that related node would get the right nodereference passed
and I would like to pass the right group in the same link....

So the question is : how can I pass the group from a node to another
related node using nodereference??

Thanks
Patchak