Hi, thanks for your help Don, Carl, Roc.
I finally could do what I was trying, this is (for the record) the way I did it (thanks to roc@ help)
-Get the url with the community_id:
... dotlrn_community__url(community_id) as url ...
-Get the community info using the community url:
array set array_with_info [site_node::get -url "${url}[apm_package_key_from_id [ad_conn package_id]]"]
This last command returns an array with all the information about the istance of [ad_conn package_id] mounted in that community.
I hope this help someone else in the future!