Thanks to Allen Laudenslager for writing about a recent experience organizing his photos:

"I moved some files into the iPhoto library using Finder, and when I opened iPhoto I couldn't see just those photos. After a lot of trial and error, I moved the files to a temporary folder under Documents, opened iPhoto and used the File/Import option to collect the photos. Now I can open them in iPhoto and use all the capabilities of iPhoto to edit them."

Note: when you install the '09 version you find the Welcome tutorial, but also take a look at the additional short video tutorials at http://www.apple.com/ilife/tutorials/?sr=app#iphoto