Use layers to position content on a page. Layers are easier to work with and change the design of than table cells. You can use layers to quickly create complex page designs and then convert the layers to tables for use in 3.0 browsers, which don't support the use of layers. You can also move back and forth between layers and tables to tweak layout and optimize page design.
You can't convert layers to tables or tables to layers in a template document or in a document to which a template has been applied. Create your original document, and convert it prior to saving it as a template.
If you are targeting 4.0 and later browsers only, you can use a combination of tables and layers and even animate your layers. For information about animating layers, see About timelines.
If you want to generate 3.0 browser-compatible files from your current file, use the Covert option in the File menu. See Converting to 3.0 version compatibility.