SQL Sets Query

PLEASE SEE my update (post #3) for a better simpler explanation!!!!!

Hi,
I need a query which is basically

(query 1)
Except
(query 2)

SQL server supports
(query 1)Union (query 2)
but I can't get the Except to work.

Alternatively,
I also tried to implement it by using the "NOT IN" but didnt work.
Background: 3 tables, accnts, Opty, Opty_postn
I want
the accounts who have 1 or more opty's at 100% (sold) before 1/1/2002 but zero opty's at 100% after 12/31/2001.
accnts has fields ID & name, ROW_ID
opty has fields acct_id, prob, ROW_ID
opty_postn has fields opty_id, close_dt

My query:
SELECT accnt.name
FROM accnt
WHERE
accnt.ROW_ID IN
(
SELECT acct_id
FROM opty
where prob = 100
AND opty.ROW_ID IN
(SELECT opty_id
FROM opty_postn
WHERE close_dt<1/1/2002)
)
AND accnt.ROW_ID NOT IN
(
SELECT acct_id
FROM opty
where prob = 100
AND opty.ROW_ID IN
(SELECT opty_id
FROM opty_postn
WHERE close_dt >12/31/2001)
)
AND accnt.ROW_ID = opty.accnt_ID

my intent was
select account.names
where id
is in set(prob = 100 & sale before 1/1/02)
but not in ( prob = 100 & sale after 21/31/01)
SO ,the accounts which have sales both before and after get counted. But I want only those accoutns which have sales only before 1/1/02.
I hope i explained this right.
Thanks in advance for your help.

Ash.