In your Pictures folder, there should be a single file called iPhoto Library (or something to that effect). Right-click on it and you should have the option to Show Package Contents.
Having said that, iPhoto's not designed for people to be rooting manually through the files. It's a pain in the butt to find your photos that way, and you always run the risk of screwing something up (if you accidentally move a file instead of copying it, etc).
If you want to email pictures, open iPhoto, highlight the pictures you want, then click the email button. It'll even give you the option to resize them.
If you want to upload pictures using the web browser, the browser (at the bottom left) should have a Media selection area that lets you easily find music, photos and movies on your Mac.
Worse comes to worse, select the pictures and iPhoto and drag them to your desktop, do whatever, and then delete the pictures.