negative queries puzzle

hi all,

here's a query i've never been able to improve:

i have an old data set and a new data set - in this case uk postcodes
with eastings and northings. i want to extract the new and changed
postcodes from the new set. to get the changed entries i use a join and
it works okay:

SELECT n.postcode, n.easting, n.northing FROM v_postcode_new n,
v_postcode_old o WHERE n.postcode = o.postcode AND (n.easting <>
o.lattitude OR n.northing <> o.longitude);

but then to get the entirely new items out i use a sub query which takes
for ever

SELECT DISTINCT * FROM v_postcode_new WHERE postcode NOT IN ( SELECT
postcode FROM v_postcode_old ) ORDER BY postcode ASC;

does anyone know of a quicker way to accomplish this? i guess there
must be some cleaver way around it, but it's beyond me.

thanks,
jinn