Yes supply the physical URL as your source. Be warned though, some sites now employ "frame buster" scripts that, if the site detects its loaded in a frame, it causes a new window to spawn void of your frame.
Read this if you want to know how to get a correct reply for your question:
^^Took that from planoie's profile^^
^^Modified text taken from gbianchi profile^^
Technical Editor for: Professional Search Engine Optimization with ASP.NET