http://www.eggheadcafe.com/community/asp-net/17/10324133/how-to-add-ajax-tools-to-form-controls-in-a-web-form.aspx
Follow this steps-
1. Open Visual Studio Web Developer 2010 and create a new ASP.NET Web Form website or Project. Open the Default.aspx file in the visual Editor
2. We’re going to create a new toolbox, by right clicking the toolbox tab and choosing Add Tab, Name that Tab Ajax control Toolkit.
3. Right click beneath our newly created Tab and select the menu option Choose Items… once you see the Browse butting, browse to where we saved our extracted files earlier, I saved them in the Desktop section of my computer. Pick the ajaxcontroltoolkit.dll and click ok button to close the choose tool box items.
4. It should take a few moments to load, once it has finished loading you will see you new Tab Named Ajax Control Tooklit
5. Now you can drag and drop these control same as other .Net controls.
Hope this will help you.