If you keep your photos in iPhoto AND in a separate folder in finder, then yes, you use twice as much space. Just import then and keep them in iPhoto and you will be fine.
The Originals are in their own special place in your iPhoto library. Users are not meant to go there -- corruption will ensue. If you want the original, in the iPhoto app, choose "Revert to Original" in one of the menubar dropdowns (I'm not at the mac right now, so can't be sure, but it is probably under "Photo"). If you want to save your edits, then duplicate the photo before you "revert".