Client-sided Hide/Show of controls on Webpage depending on user selection

Need help in including Javascript/Css code in an existing page of an ASP.NET application created by Ironspeed designer (using C#). The Project is to Hide/Display controls in the interface dependning on the selection of Drop-down boxes and activation/deactivation of a checkbox made by the user without a postback to the server. Existing compile-able ASPX, C# code will be provided (for Visual Studio) Details of the project are described in the attached Spec.