Basicaly you are making more work for yourself. By the time you find the right tool and download a copy of it and all of that good stuff you could have given your customers computer back to them. As someone who has spent a very long time in customer service I can tell you most customers would rather make the 5 to 10 minute phone call then have you screwing around for a few hours trying to crack the password. Customers want their systems back in as timely a manner as possible. Im not sure if it will work in your case but there is a program that can be found with a simple google search for password revealers.

There is one question that bears asking here. Why did the person not just have the ISP help with the setup? It just makes more sense to me. Most ISPs will supply an instalation disk that will take care of all of the configuration.