Okay, Question 1:
I recommend not using a query. Use the ApplyFilter command instead:
Private Sub YourButton_Click()
Dim stFilter as String
Dim stMsgRslt as String
stMsgRslt = Msgbox ("Your message here"...)
stFilter = "[PO]= '" & stMsgRslt & "'"
DoCmd.ApplyFilter , stFilter
End Sub...