1) Wildcard in Query form a textbox form- some null values. 2) Hide Report Details section based on Form input yes or no

1)  I have a database that I have written a Report that calls a Form that runs a Query.   The query looks at a date range (range is supplied on Form by user), Event (Supplied on Ofrm by user, and Mailbox numebr (to be supplied on Form by user).  I can get this to run correctly using the date range and event selection.  I cna not get it to run with the mailbox in anywya or form.  the mailbox field CAN have null items.  I tried IIf(ISNull([table].[mailbox])=True," ",[table].[mailbox]) in the Field box of the query wiht Like [Froms]![formname]![mailbox] in the Criteria and a default value of ="*" in the Form.  I get nothing in the data and also prompted for the Mailbox value.  I also do not wnat to have to input anything for the mailbox value (find all records meeting the other criteria.  Any suggestions?

2)  the other thing I am trying to do is put an option on the Form to hide the details on teh Reprot and jsut show the sumamry count.  The count works, but can't figure out how to make the detail section hide if a radio button is selected on the Form.  Need this due to amoutn of detail for some reports.

Thanks!