I have a program, it's called sam inside. The issue with this is you need to be admin to hav access to sam files, but if you're not boot up linux from a CD and copy the sam files from their directory and then run them through this program. It tries guessing and eventually brute forces.
http://www.google.co.uk/url?sa=U&start=1&q=http:/...nside.shtml&e=9901