Which object you can select depends on the kind of control you are creating. If you intend to launch and run Excel, drop an automation reference. If you want excel in a container, consider using an activeX document. You can also instert IE in the container and point it to an excel file.
Take a look in the shipping examples for excel for a working example of how to make the activex calls. Excel programs are very numerous on the web. Go to<a href=" http://search.ni.com/?col=alldocs&layout=TechResources&ql=a">Advanced Search</a> and search just the example programs.