Thanks for response.
If there is no need to install this then why there is no any Ajax enabled templet when i create new website.
And if i working with my old project then in this these controls are not working.
eg. there is no effect of rounded corner extender on panel.
For the AJAX Toolkit you do need to install the dll. You can drag the DLL into your toolbox and have it populate the items. In your project you will want to right click > references then browse to the appropriate .dll (ajaxtoolkit.dll) and then Visual Studio will load this into your APP_BIN folder for you.
For exitsting projects it is easy to add the functionality needed by simply adding a ToolkitScriptManager to the page, then encapsulating your ajax modules in an update panel (which is built into the visual studio AJAX section [asp:updatepanel]
I do not ever need to do anything inside of the web.config file for this. Looking through my files it seems as though you don't need any additional configuration but its possible that visual studio handles any additions needed once you create the reference from the IDE.
No you should not have to add anything to web.config. If there are additions required then visual studio has always taken care of them for me, but in reviewing a few config files from my past projects that use this there is nothing referencing the ajax frameworks.