I need a motherboard that I can assign a password to the BIOS and have it expire in a certian period of time.
I don't see how this would help in any way. What do you think you need this for? You can set a BIOS password and change it whenever you want. But do you really go into the BIOS that much? Once I have a computer working how I want, I never look at the BIOS again until my next upgrade. I would hate to have it force me to change the BIOS password every 3 months.
Also, like what was said earlier, the BIOS password can easily be cleared. So if you are that concerned you should also put a padlock on your case so it can't be opened up.