I was searching for a way to send emails to user in a customers group.
I found a easy way to do it:

Enter in your database (through MySQL or other) and enter in the table "query_builder". Insert a new values row with this values:

Query_id: the-next-id-number (7 to me).
query_category: email
query_name: group1 (the name of your group)
query_description: a description of your group
query_string:
Code:
select customers_firstname, customers_lastname, customers_email_address from TABLE_CUSTOMERS where customers_group_pricing = '1'
(1 is your groupīs id number. You can find that number in the table "group_pricing)

...and thats all ;) Repeat the script to add all groups you want.

Tell me if it works! ;)

sorry for my English... if anyone wants to do a better translation... please do it.