Hi Shelley,
This article on using "radio check boxes" includes two downloads with code you can examine for each type of PDF form, AcroForm and LiveCycle Designer. This does not discuss greying out fields but does show how to create mutually exclusive check boxes that perfrom like radio buttons- only one choice allowed.
Radio Check BoxesThis next article discusses how to disable, or grey-out fields in both AcroForms and LiveCycle Designer PDFs-
Disabling FieldsHope this helps,
Dimitri
www.pdfscripting.com