Can you help me find a free graphics/images/design/whatnot program for Mac?

I need to take an image of a map (which I already have) and add dots to it in specific points. And either text or numbers to label the dots. It needs to look professional.

I have a MacBook 10.4.11, so I downloaded Gimp but it doesn’t open, Paintbrush didn’t either (as recommended in this thread: http://www.fluther.com/disc/51861/whats-the-best-free-drawing-software-for-mac/), and Image Tricks only adjusts images but you can’t seem to add such specific things to them (like iPhoto and others)....

Help anyone?