ASP.NET AJAX Control Toolkit is an open-source project from CodePlex and built on the top of the Microsoft ASP.NET AJAX framework. These controls are designed using concepts that are familiar to ASP.NET Web Forms application developers. Using the Ajax Control Toolkit, you can build Ajax-enabled ASP.NET Web Forms applications by drag and drop Toolkit controls from the Visual Studio Toolbox onto an ASP.NET Web Forms page.
How to Ajax Control Toolkit ?
The first step is to download the compatible version of the Ajax Control Toolkit. You can download the latest version of the Ajax Control Toolkit from CodePlex.
After downloading the Ajax Control Toolkit compressed file, right-click the file and select the Extract All menu option.
Launch Visual Studio and create a new ASP.NET Web Forms project or website. Open Default.aspx in the Visual Studio editor.
Create a new Toolbox tab by right-clicking the Toolbox and selecting Add Tab . Name the new tab Ajax Control Toolkit.
Right-click beneath the new tab and select the menu option Choose Items... Click the Browse button and browse to the folder where you extracted the Ajax Control Toolkit. Pick the AjaxControlToolkit.dll and click the OK button to close the Choose Toolbox Items dialog.
For more information about how to integrate Ajax Toolkit with your Visual Studio : http://www.asp.net/ajaxlibrary/act.ashx