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In the past, I remember that FileVault asked you to set up a master password when you turned on FileVault to, if I'm correct, start into OS X if you didn't remember the admin password. This was on Snow Leopard, because on Mountain Lion and Lion, Apple gives you the master password, only available if you use FileVault
Not if you have as Snow Leopard
We're assuming that the user's hardware signature line is correct and accurate, the OP may very well have upgraded to Lion and/or Mt. Lion.
Or, you can just use the Google machine on the Internet device and search for the article that explains how to reset the admin password for Snow Leopard - http://support.apple.com/kb/HT1274
Kbase searching = awesome