[AccessD] Filter form recordset by combo box

Hi, all. I've got a problem that I can't sort out by myself.

I have a database being used by a data entry clerk. She needs to see a list 
of information by department number. I created a simple form with an unbound 
combo box where she selects the department she wishes to view. She can then 
do several things based on that selection - view it for printing, export it 
to Excel, or open a form with that department ID as the form's criteria. 
Here's the rub -- when she views the list on a form, I'd like to give her 
the ability to change departments on the fly. So if she's looking at a form 
filtered for DeptID 104735, she could use a combo box populated with all of 
the department numbers to change the recordsource for her form's data. The 
combo box value on the orignal form where she picks the department number 
provides criteria for the query on which the second form is based. I think 
perhaps if I could set it up so that the second form's recordsource was set 
directly from her choice on the first form rather than a query it would be 
easier for her to change it but I'm having trouble doing that. If this makes 
sense, has anyone got any good ideas for me?

Thanks!
Gina