namespace name 'Excel' does not exist in 'Microsoft.Office.Interop.Excel

Hi Team, I am getting error  namespace name 'Excel' does not exist in  'Microsoft.Office.Interop' I tried adding Add Reference >.NET>Microsoft.office.Interop.outlook as solution but could not find Microsoft.office.Interop.outlook  in Add reference. I am using visual webdeveloper 2008 express edition. Please help me in this. Thanks, Kranthi