Upload an iframe? 
You want to show a page in an iframe in the portal?
Just
- create an html-file, where you include the code for the iframe through simple html-code (google for "selfhtml" if you don't know how to do that),
- upload that file into the portal,
- create an document-iview that points to the html-file and
- put the iview into a role to add it to the portal navigation, so that users can access it where you want it to be.
Regards,
Steffi.