There are a lot of people who just can't draw with the mouse (I can't). That's why I've created DrawAid. It's a simple yet very useful program. It allows you to load an image, adjust its transparency, zoom it, move it... Once it's set you can use any painting tool from MS Paint to GIMP or Photoshop to draw - the on top image "ignores clicks"; it passes them to the application behind.
Or download the portable version for Windows Live from this link: http://sites.google.com/site/xenodesystems/drawaid-siv
...Yes DrawAid is now portable thanks to James Berry from Xenode Systems - be sure to visit his website at http://www.blogxenode.tk/