Filtering on Date Fields in a Pivot Table

[John]

Does Anyone know know how to use FilterMembers on Date
Fields in a PivotTable? In JavaScript:

var v = pivot.ActiveView;
v.ColumnAxis.InsertFieldSet(v.FieldSets("ShipType"));
v.RowAxis.InsertFieldSet(v.FieldSets("InvDate by Month"));
var cf = v.RowAxis.FieldSets(0).Fields
var f1 = v.FieldSets("InvDate by Month").Members
(0).ChildMembers("2004")
cf.FilterMembers = Array(f1)

And fails on this last line. Actually I want to filter on
the Current Month, but was trying this first.

Any advice would be appreciated.