thanks for delayedinsanity for the reply...

i finally manage to get the query that produce the result that i wanted:
here it is .

SELECT rt.roomtype, rt.roomprice
FROM roomtype rt
INNER JOIN rooms r ON rt.roomtypeID = r.roomtypeID
WHERE r.roomID NOT
IN (

SELECT roomID
FROM booking
WHERE checkin >= '2010-04-01'
AND checkout <= '2010-04-06'
)
GROUP BY rt.roomtypeID

however, i did really appreciate your helps.
thanks again. Cheers! :D