Have you tried Booting Up on Safe Mode?
If the pc was set up to work directly off a Server from it's begining point, then chances could be that the Owner acct: does not have a pwd. And if this is so, then when you try booting up in safe mode the os automatically gives you the option of choosing to log in through the Administrator acct: (which doesn't have a pwd) IF this works out for you, through this acct: you'll also be able to change the way you log in and to remove anyones' pwd's!
(i've tried the ubcd on Xp home/Pro/Media and Vista home edition for "Killing Time" purposes, to remove pwds and It Has worked, so maybe....... you're making a left turn somwere in there when needing to make a right, knowaming?

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Good Luck!