Able to access parent window using 'tab' buttons, even using modal dialog popup windw

1) Script Title: Able to access parent window using 'tab' buttons, even using modal dialog pop up window.

2) Script URL (on DD):
http://www.dynamicdrive.com/dynamici...dhtmlmodal.htm

3) Describe problem:

I am using Modal Pop-up window to restrict user to submit first servay data, I am not able to click on parent window but if i use tab button then able to hit links from parent window..

does anyone has solution for this....

thanks in advance..