try this
www.telerik.com/community/forums/thread/b311D-bedgta.aspx
www.telerik.com/help/aspnet/grid/grdmakepostbackajaxrequestfromusercontrolwebformmasterpage.html
demos.mcmscontrols.com/aspnet/Grid/Examples/Client/PostbackOnClientRowClick/DefaultCS.aspx
http://www.google.com/search?hl=en&sa=X&oi=spell&resnum=0&ct=result&cd=1&q=RadGrid+control+Ajax+postback&spell=1