Good question. I know it's pretty easy, but unfortunately I'm stuck on my windows machine at work. (Yes, I know I should be doing work...)
Couple of different ways off the top of my head...
I would imagine you could sort by file type (.jpg). If you have all your photos and videos in one folder, open that folder and then try sorting. There should be an option in the top Finder menus (the menu bar at the top of the page.)
If you have your jpg photos stored in lots of different folders, you could try creating a "smart folder." This is a little more advanced, but pretty easy. The Finder menu will allow you to create a new smart folder on your desktop. The folder will look different (purple with a little widget in it). When you open that folder, you can basically create a query to that will have the folder only display certain items. For example, you can have the folder display new files that were created within the past week. In your case, you could have the folder display any files with a .jpg extension that are located in certain folders. You can then click and drag those items directly into iPhoto. The smart folder doesn't actually contain the items it displays, it simply shows you the results of your query. Like I said, I little more advanced, but really user friendly once you wrap your head around the concept.
I'm sure there is a really easy solution - wish I had my Mac with me.
