You said you were looking for matches. Now you are saying you are looking not for the matches, but for the things that don't match. That is very different!
Funny you should ask this at the same time as someone else asked the question on this thread: viewtopic.php?f=1&t=13565
An alternative it to perform a full outer join between the two tables. Whichever columns contain NULL is an indication of the record being missing from that table.