>>>>I am talking about web application not VFP. you know what i am talking, right.
>>>>
>>>>Thanks
>>>
>>>Are you talking about something like Modal popup extender (AJAX)?
>>>
>>>You better ask your question in .NET forum, I have some other ideas...
>>
>>I don't think my question is .NET specific it is general web question.
>
>You're right, but you asked your question in VFP Chatter forum and I'm not sure it's the best place for this kind of questions.

It is the best place... and the answer is: javascript, lots of it :). I'd look at webpage's source, before and after such a popup has come up. My guess is that it's actually a flat on-the-page object, i.e. it lives inside the webpage and can't float out of it - try to scroll and it scrolls with the page - it only has a higher z-order than the other objects on the page. It all lives in the browser.