Resizing photos in iPhoto:
1. Chose the photos you want to resize (for example, for a craigslist ad) by clicking on them. If you are using more than one, hold down the command (apple) key while you click.
2. Go to file -> export.
3. Select File Export (shown as File Exp...) from the bar on top of the little window.
4. Select the type of file from the drop-down menu. The pre-selected choice is "current", meaning the same type file as you are exporting. You will probably want to choose jpeg from this list.
5. Choose the size you want. "Medium" is the default.
6. Select a filename if you like, or just let it go with the current name.
7. Click on "export". At this point you get to choose whether to accept the file name (or type in another) and you select the location to store the resized photo.
I have offered more detail than you'll probably need. That's my tendency, just in case.
The reason I offer this tip is that I was frustrated for a while when I wanted to resize photos. I searched the help files and the spotlight search and got nothing useful. It's strange that this method does not show up when one searches for "resize". But it's typical of help files. I swear, the guys who write them have absolutely no idea what we will actually need to know.