Textbox to appear upon ddl selectedchanged

Hi, I need the textbox to appear when the user choose 'Others'. But when I chose 'Others' the textbox doesnt appear.. here is my code:
Protected Sub loadFile()
          //web service declaration
            Try
       //binding
                ddl.Items.Insert(28, New ListItem("Others", String.Empty))

            Catch ex As Exception
                lblError.Text = ex.Message
                lblError.ForeColor = Color.Red
            End Try
& ...