There are shedloads of CDs readily available on ebay that will retrieve passwords. So long as it is not a locked domain.

But in many respects the most complete route is a new hard drive install OS, install good antivirus and then connect the old one as a slave.

For future reference just put programs on one hard drive, and keep all data on a bigger separate drive. Keep a partition of that for a clone of your OS (using something like "Ghost" or "Driveclone"). Also when you download a program save it to a download programs folder on the data drive and run to install from there.