Rhonda,
You'll have to forgive my ignorance, but I am unfamiliar with the Web Premium CS3 tool of which you speak. Reader Extensions is a feature that can be added to the LiveCycle ES installation at a give location. Someone can correct me if I'm wrong here, but I believe you need LiveCycle ES in order to reader extend PDF forms.
Any forms that are developed in designer, no matter how sophisticated they may be (dynamic in nature, with all kinds of business logic goodness built in, and buttons to do everything from print to submit via email), will just view as a static PDF with the free reader tool (ver 6.0, 7.2, 8.0, etc...). Reader extending a PDF file is an extra step that is done after the form has been completed (completion of development). LiveCycle ES allows for a user to perform many of the functions that Acrobat allows (filling in of forms, and submitting them) with just the free Reader client being loaded on the end users machine. Of course the form must be filled in through the LiveCycle workspace tool, and would appear to be a static PDF file if the form was downloaded and viewed with Reader outside of the workspace tool. Again, the exception to this being if the PDF has been Reader Extended.