Hello,
@sbillard, acrylian: thank you for your messages
@acrylian: no need for sorries

dev work is wonderful and support is a plus!
Having read "How to use the Dynamic Albums feature" and after some thinking I understand what sbilliard suggests goes along the lines:
1.- have an album (or set of photos, depending on admin preferences) tagged
e.g. /gallery2012/gallery2012b [family trip] tagged as familytrip
2.- create a dynamic album and have permissions assigned to it for a group
3.- repeat 2.- for as every different group permissions must be granted to
I prefer to set it out this way so that other reading this topic can easly implement the procedure.
So basically it would consist of creating as many different dynamic albums from a static album. That way, different group permissions may be granted to a same album.
To be more precise, I don't think there is a need to tag
/gallery2012/gallery2012b [family trip]
since as a dynamic album can be created if the search term consists of the album title - easy identification.
Please, [correct|add|...] to your liking.