In Visual Studio 2005 the Component Tray has changed. To add non-visual controls to the form, you must open the Component Designer surface of your Web page. To do this, right-click your Web Form in the Solution Explorer (or right click the Web Form in design mode) and select View Component Designer from the shortcut menu. This opens the Compnent Designer for your web page.
You also need to use the Component Designer to add event handlers (other than Load) for your web page. After you view the Component Designer for your web page, you can click the Events lightning bolt on the Properties Window to view web page events for which you can create handlers.
Note: In order to view the Component Designer, you must have chosen to place the code for your Web page in a separate file. You cannot access the Component Designer from Web pages that use inline code only