First you need to convert the image to vector. Illustrator uses vector art for patterns. If you want the pattern to be an image you should use Photoshop. It would be easier to just find a pattern that has already been created. Did you try the link Doug shared?
I'm not aware of any in the patterns supplied with Illustrator, but you can quite easily find some on the web or make your own. I just tried a few of these and they look ok: