I want to get the tab to move from the last box in the first subform to the first box in the second subform. At the moment it goes from the last box in the first subform back to the first box in the same subform.I cannot do it with the tab index. Can it be done using code?

I haven't tried this myself but you could try this.
On the afterupdate or lostfocus property of the last field in your first subform set it to

DoCmd.GotoControl Forms!NameofMainForm!NameofSubform2.Form!NameofCon trol

HTH

Or just Forms![MainForm]![NextFieldName].SetFocus

HTH,
David R