UpdateProgress on top and dimming of page

I have seen this used in several places but have yet to see how to do it. When a process is initiated and the UpdateProgress is shown, it is shown on top of everything else on the page and it dims the whole page and everything else on it to bring attention to the progress control. I am assuming that it is just some layer made to be transparent but like I said, I can't find anything about it. Can someone give me some more information or better yet, point me to a tutorial?

Thanks in advance!

Try to take a look at this reading to?get?some?ideas?-?http://ajax.asp.net/docs/overview/UpdateProgressOverview.aspx#HowTheyWork.
You?can?implement the progression through?threading?sleep,asp:UpdatePanel and asp:UpdateProgress.
Wish the above can help you.