The in-page view in Google Analytics shows the website in an IFrame and overlays the statistics of link clicks. How is this done to track and show clicks (or entered data) for textbox ( elements)?
In order to track the use of the textbox you need to add event tracking. You can find a detailed guide here: http://code.google.com/apis/analytics/docs/tracking/eventTrackerGuide.html.
For example, I got this snippet of code:
Once you've set that up you can see clicks, but you can't see entered data via the overlay. To do that you'll have to look at the event reports.