Modal Popups

Hi,

I was browsing this website earlier on today(www.fsms.co.za) and I noticed they had the exact same thing as the one I want to use for my asp.net application. They used modal popups to display messages as Messageboxes on their page..

I also want the same for my page, can anyone please tell me on how I can do them. Here is a sample of what I am talking about



I hope I can get help on this, thnx