Quick question about users/groups

[tkx]

What happens if a user is in 2 different groups? Which permissions does he get?..  Also, is there a way that you can set permissions for each group on each album?

Here is my scenario.

I have some public photo galleries where I say that people can upload photos to.  If a user sets up a personal gallery, and then says he wants a group to be able to upload photos, set comments, etc.    If I put these people into a group that allows comments, etc.  Will they be able to post comments into EVERY album, or how do I set it so it only applies to that album?