From the last control, try something similar to this in the KeyDown event of
that control.
If KeyCode = vbKeyTab Then
Me.NameOfSubformControl.SetFocus
Me.NameOfSubformControl.Form.txtField1.SetFocus
End If
To go from one subform to the other, the SetFocus should be modified to
Me.Parent.NameOfSubformControl.SetFocus
Me.Parent.NameOfSubformControl.Form.txtField1.SetFocus
Essentially, you have to go up to the main form, then back down to the other
subform.
NameOfSubformControl is the name of the control on the main form that holds
the subform, not the name of the subform. To get this name, open the main
form in design mode, open the Properties sheet, and click on the subform ONE
time. The properties sheet should show the name of the subform control. If
you click on the subform a second time, you'll be in the subform and the
properties sheet will show the name of the subform, not the control holding
it.