Special Criteria using the Date Field

[Mark]

Hello,

I created a warranty program using Access 97 and I need
help on one of my queries. I want to be able to look up
products that were returned during a particular month. I
can do that with no problems. However, I would like to
automatically subtract 18 months from the month that
product was returned so I can tell if it is within the
warranty period. I can manually get it to work but it is
a pain to do. Can anyone help. I would appreciate any
comments.

Thanks!
Mark