I guess when you say "with ICQ" you mean that icq is not blank? Then maybe this:
Code:
SELECT username FROM user WHERE icq > '' AND posts > 1
and change to posts < 1 for the second query. That leaves out users with exactly 1 post, I'm not sure if you meant to do that or not. I'm guessing you meant "one or more posts" for the first query, in which case you'd use posts >= 1.