Hello, I moved this discussion to the Photoshop Elements forum. You should better find what you are looking for there.
You can use either organizer or iphoto. If you prefer to keep using iphoto to organize your photos you have two options:
1. Set PSE as your external editor and send the photos from iphoto to PSE for editing, then save them without making any changes to the name or format (you may need to set the editor preferences>saving files>on first save to save over existing file) and iphoto will remember your last saved edited version + original.
2. Export the photos from iphoto to the desktop, use File>Open in the editor to open the exports for editing, save with a new name and import the edited photos to iphoto as new images. This way you can save as many versions and different formats as you like.
Or you can use the organizer instead. If you aren't sure, I would suggest exporting some photos to the desktop, putting them where you plan to keep them and then using File>Get Photos>From Files and Folders to make a test catalog to see which you prefer. Eventually you will want to choose one or the other.