Access 2007 – Checkbox Control

Novice Here. I am looking at providing a few check-boxes on a form. When one is checked a textbox control would change its control source. For example, if a user selects the first check-box (entitled First Name) the control source for a textbox would become [table “” not found /]
.[fname], if they select the second check-box (entitled Last Name) the same textbox would change its control source to [table “” not found /]
.[last name]. It seems like it should be simpler than I am trying to make it, but I am having issues finding references.

Thanks,

Joel