Use the following script to pop up the window after some fixed time period...
just call the function myPopup(ans); after the fixed time..
'ans' Variable will contain the choice of user(i.e. want to continue or not)...
Create on jsp file named 'dispDialog.jsp' ask for user choice and a submit button...
add the following code to return the 'ans' to parent window..
I think this will help...