Many to many data retrievel

Hi Folks,

Hi have a Problem getting a certain query to work. Here is what the problem is:
I have 3 tables TableA, TableB and the link table TableA_B all connect in a many to many relationship.
Now I have 2 (or more) keys from TableA and I need to find the corresponding entries in TableB.
So far so easy, but:
I only want the entries in TableB that have key relations in TableA_B for both (or more) keys.

Example:
A group table and a user table in a many to many relation. Now I want to list all users that are both in group A and group B.

How can this be achieved??
Thanks for your help!!

migo