Text box value : 2
Date1 : 16 Jan 2010
Date2 :----
Well, based on this:
1. Hook a onchange event to textbox1
2. based on data entry in textbox, onchange would get fired once done
3. in your onchange event, create a random/todays date and show it in another textbox2 or in a date field
4. at the same time, add two days or any other manipulation to textbox2 date and show this new one in textbox3.
Try!