The AlwaysVisibleControl Extender provides the functionality of placing the control on ASP.Net web page that remains visible and floating over the page content whether you are scrolling the web page or resizing the browser window.
AlwaysVisibleControl belongs to the AJAX Control Toolkit that works with AJAX extensions. ScriptManager is compulsory on top of the web page to work with AlwaysVisibleControl Extender.
You can associate the target control ID with AlwaysVisibleControl that you want to float over the web page. Also you can set the other properties of the AlwaysVisibleControl to fix the position of target control vertically and horizontally.
Sample here : http://download.microsoft.com/download/f/7/a/f7adf2b4-6554-4027-bac6-c853bc0a4f9d/HDI-ACT-AlwaysVisible-CS.zip