When you use the open report method in the button code, you can use either the 3rd argument, which is the filter argument (the name of a query) or the 4th argument, which is an SQL WHERE clause without the word WHERE. So it might look something like this:
DoCmd.OpenReport "Sales Report", acViewNormal, ,"[SalesRepID] = " & me.txtSalesRep
which opens the report and restricts the data to field SalesRepID being equal to the value of a form control.
JimD.