First of all when you are going to install Ajax Control Toolkit in VS-2010, then first thing you have to remember - in visual studio 2010, you can install the Ajax control toolkit version 2 also but that will create some problem. (At the time of using these controls) So better to use this one you must have to use Ajax Control Tool Kit 4 in Visual studio 2010.
You can download Ajax Control Toolkit 4 form this link : Click Here For Download
|Add New Tab|
Step:2 By right click on the made tab (like - Ajax Controls) select the - "choose items" for choosing your .dll file from your computer.
|Choose Your DLL File|
|Like This Way You Need To Attach|
|Show the Components.|