Dynamic forms arent really that hard. The simplest way is to have a routine that reads some datasource (db,xml, text file) and converts values in it to form fields - those values should tell it what kind of control (textbox, checkbox, checkbox list etc.) to build and add to the page at run time.  Then you need a routine to run on submit and saves those values in some format (again db, xml, text file)

I think the hardest point in building dynamic forms is having an online form builder