Ok. cual version de autocompletarextender de ajax debo usar ya que estoy usando visual estudio 2005, ya que coloco el control y me da este error
Indirect reference is being made to assembly System.Web.Extensions version 3.5.0.0, which contains 'AjaxControlToolkit.AutoCompleteExtender'. This Project references a prior version of System.Web.Extensions version 1.0.61025.0. To use 'AjaxControlToolkit.AutoCompleteExtender', you must replace the reference to System.Web.Extensions with version 3.5.0.0 or higher.