>I want to display a grid on a form, with records that only meet certain standards. I've tried setting the record source type property of the grid control to 3-query and 4-SQL statement, and specified the appropriate path to the query or the SQL statement in the grid's record source property. My grid is always empty. What am I doing wrong?

Firstly, base your grid on cursor (another possibility is to base it on p-view). Then repopulate this cursor anytime you change your criteria values. Note, that repopulating the cursor should be done carefully like this:
Select MyGridCursor
ZAP
Select ... Where (your criterea here) Into Cursor tmp NOFILTER
cDbf=dbf()
Select MyGridCursor
Append From (cDbf)
Thisform.Grid.Refresh