Ooooh eck....
Tried L0phtcrack out on my 2000 machine (for legitimate purposes I hasten to add).. 7 passwords on there in total, it had 5 of them within 5 minutes.....
Its doing 650,000 keys per second and all alphanumeric passwords will be checked within 3.5 hours. Figure less than 2 hours on average to find any password. Hell it isn't even a fast machine....