In all honesty, if there were a way to alter the admin password through the BIOS, etc it would constitute a colossal security flaw and be a nightmare for us all...
My recommendation would be to attempt to contact the old admin and ask him for theinformation. If he left on good terms (or has much in the way of integrity) he'll offer it to you. If he's reluctant and getting this resolved will save you time and effort, you could even try to get it authorized for him to come in for an hour as a"consultant" to get it removed. I'd never *dream* of making a former employer do that, but it takes all kinds....
If there is no way to reach the old admin and no one else previously that knows the information, you're really stuck. In that situation, you'd probably be better setting the machine up again anyhow. Take notes on the hardware & its settings, the services running, the networking configuration and software. Back up any data through what means are available (this may be limited depending on your circumstances...since you can't log on as admin).
The previous answers are exactly right about getting past a BIOS password. If you can see the jumper on the mobo or have your manual available (or online), you're all set. If not...pull the battery.
Good Luck!
