Here is one way of doing it.
Photoshop tutorial: http://tutorialoutpost.com/count/5261
This can be done with fireworks or other similar programs just change the grayscale of your image and zoom in and start coloring. Or use the magic wand to highlight specific areas for faster painting.
This one is a little more difficult but also a little more professional technique.
Photoshop tutorial: http://tutorialoutpost.com/count/5355