I just tried the Ophcrack Live CD and I think it's GREAT !
It is a bootable Linux CD-ROM containing ophcrack 2.3 and a set of tables (SSTIC04-10k). It allows for testing the strength of passwords on a Windows machine without having to install anything on it. Just put it into the CD-ROM drive, reboot and it will try to find a Windows partition, extract its SAM and start auditing the passwords.
More details on: http://ophcrack.sourceforge.net/