Best Mac program to take several screen shots and combine them into one long image?

[skydakotasky]

What program for the Mac (Leopard) would be equivalent to Microsoft paint in the way you can open a blank document, paste a screen shot/image on it, then paste another while being able to move the second image around easily (to put it underneath the first image, lets say). I have Pages, but I have 5 images of a conversation I want to piece together and I can only get 3 on a page. That and I want to be able to save the big image as an image file, not a text/pages file.
So, best free program/program that has a free trial?