Steps To install Ajax Library in VS 2005:

1.) Install "ASPAJAXSourceCode.msi"

2.) Install "ASPAJAXExtSetup.msi" (Download from http://go.microsoft.com/fwlink/?LinkID=77296
or
http://www.microsoft.com/downloads/details.aspx?FamilyID=ca9d90fa-e8c9-42e3-aa19-08e2c027f5d6&displaylang=en)

3.) Run 2005 -> New Website -> Ajax Enabled Website ->
In tollbox create New Tab "Ajax Controls" ->
Right Click on this Tab and Choose items ->
In ".NET Framework Components" Browse and choose "AjaxControlToolkit.dll".

4.) All controls will be added.