SQL Query
INSERT ubbt_USER_GROUPS(

SELECT ubbt_USERS.USER_ID, 4
FROM ubbt_USERS
WHERE ubbt_USERS.USER_ID NOT
IN (

SELECT ubbt_USER_GROUPS.USER_ID
FROM ubbt_USER_GROUPS
)
AND ubbt_USERS.USER_ID <>1
)

assume you have mysql 4.1 or greater and your table prefix is ubbt_