Although arne's solution will work, I don't like to use subqueries. Access doesn't optimize them well so they can be slow and they are hard to read in QBE view. Subqueries are fine if the BE is SQL Server but I still find them hard to read in QBE.
I would go with an unmatched query as Colin suggested but the problem with this is that Access will not return what you expect when you use a LEFT join and the criteria is on the RIGHT side table. Therefore, I create a query for the rightside table with criteria to limit the orders to the past 30 days and then use a left join of the customer to the query.