Seashore is a nice, free app for OS X that can handle the same things that MS Paint does, and more. I'd recommend using that. iPhoto will not let you type on the photo, but you can add comments, etc.
Well, there's always Gimp.app, but that requires X11 which is usually installed in recent versions of OS X. If not, you can use the installation discs to install it.
It depends on opinion, of course. I believe that you can do that in Seashore, but I don't have the app in front of me now, so I can't tell you how. Seashore's main advantage is layers, but it also can save in more formats than Paint, use different brushes, etc. It more closely resembles a low-power Photoshop than Paint.
Originally I was going to suggest GraphicConverter but I wasn't sure if it allowed you to write text to pictures which was why I left it out. But yes, if it does that then that's another option.