Well, usually it's pretty simple to bypass the BIOS password if a person can actually open the computer. Most (all ?) motherboards have a jumper that returns the BIOS to it's original settings, erasing passwords, etc. So you need to keep the case secured. Some cases are lockable, but for those that are not, you can replace the standard screws with a type that requires a special screw driver. Alternately, you could use a desk that has a lockable compartment for the CPU unit.

Hope this helps.

Chris