Picture inside a mosiac? What software to use?

I saw a mosaic photo today which I thought looks really cool. From the look of it, it appears to be just a simple mosaic. Upon closer inspection it's actually tiny photos forming the mosaic photos. That seems pretty cool, does anyone know which software they used to do this?

edit: just found this but not very great

http://homepage.mac.com/knarf/MacOSaiX/Download.html

hi - did you find a better one than this since the time you posted?