Add Days to Date/Time Field

I have a form with two date fields. One is the Date Submitted and the other is the Date Required field.
The first thing I would like is that the Date Submitted field will autofill when they push the Submit button.
The second thing is I would like is that the earliest date they could pick in the Date Required field would be the submit date + three workdays. For example, if they submitted their form on 02/02/2009 the first choice they would have in the Date Required field would be 02/05/2009.

Thanks in advance for any help.

EJR