1. create a tablespace ts_y.
2. assign it to user Y( make it default for Y).
--now do import like
3. imp dba/password fromuser=x touser=y file=myfile.dmp
-- NOTE:
-- this will create all the tables in ts_y
-- if there are any indexes, still in someother 
-- tablespaces that are owned by X, it will recreate the
-- indexes in that tablespace only.
-- so, use indexes=y to ignore the indexes ( indexes by primary keys, wont be ignored) and
-- recreate the indexes manually 
-- or
-- let the indexes be created in ts_X. later u can move them to ts_y