Form Filter Problem

[Parker]

I am trying to make a form to add & update a simple table
with the following fields using Access 2000: OrderNo
(Text); Amount (Currency); Vendor (Text); Description
(Text)
There is no primary key as each OrderNo may have multiple
entries in this table.
I created a query with all four fields and then made a
form based on the query.
I want the form to show only the entries for the given
OrderNo and go to a new record if there are no entries for
that OrderNo. I'm trying to use an InputBox on FormOpen
to get the OrderNo but I can't get the form to filter on
the given input. Is there a better way to accomplish
this, or can anyone help me with the coding to make this
work properly?

Thanks in advance!

Parker