SELECT name, email
FROM   members
WHERE  id IN (SELECT id
              FROM   profilefields
              WHERE  field1 = 'X' and field2 = 'Y')

SELECT
    m.name,
    m.email
FROM
    members m
    INNER JOIN profilefields pf ON
    m.ID = pf.id
WHERE
    pf.field1=X AND
    pf.field2=Y

SELECT m.name, m.email
FROM members m
JOIN profilefields p
ON m.ID=p.ID
AND p.field1=X
AND p.field2=Y