Oh an by the way, the would be like:
Select Activity.field1, Activity.field2, ... , Activity .Fieldx from Activity, Dates where activity.date between dates.start and dates.end
The problem you were having is that you have to mention every table you are going to use in the FROM clause to use the data fields later in the SQL Statement.
I think that Inner Join cassie was going for was something like this
Select * from Activity Inner Join Dates on ((activity.date >= dates.start) and (activity.date <= dates.end));
This works the same as the one I submitted earlier so you may still want to specify the Activity fields you need
Brian Coats