The Access 2000 help file has an example that's just perfect for you:
Code:
Forms!Orders.RecordsetClone.MoveLast
MsgBox "My form contains " _
& Forms!Orders.RecordsetClone.RecordCount _
& " records.", vbInformation, "Record Count"
In short, use the RecordsetClone.MoveLast method to fully populate the form's recordsource (you may get an inaccurate count otherwise), then use the RecordsetClone.RecordCount property to get the actual count.