If you're using autogenerate, you can set the fields to be hidden in the .cfg file. In the place for "form-length" -- just after the field type (alpha, numer or date) -- put "-1."
If you're defining your own forms and records, the field that Jaime mentioned goes into the html.pl file, sub html_record_form.
Yep. If you don't have the hidden fields on your form, when you add or modify a record those fields will end up to be empty. You will lose any information you had there.
This, of course, assumes that others can add or modify records on your database. If you are the only one to add or modify records, I suppose you could do without the hidden fields.
You can't do what you want to do as long as you use the autogenerate feature. You'll have to build your own html_record_form and html_record subroutines.
(Actually, I suppose you could just get by with building html_record_form and let html_record autogenerate.)
Anyway, if you build html_record_form, you would add something like