Can I import Picasa files to Elements 20 w/o access to Picasa?

The Elements Organizer is only a database catalog of the files stored on your computer.  So, you import the files from the storage location.  If you are new to Elements, when you first launch the Organizer, a new catalog will be created and you will be given the opportunity to import all of your media files. I am not familiar with Macs, so can't give you the exact details.  But take at look at this guide.