Originally Posted by niharikaananth
So it would be appreciated if anybody could show the possible way to find out the original MAC address(as written in BIOS) of the LAN computers.
You can't from another host (i.e. for the purposes of access control). You'll see the MAC address that the system is presenting to its peers.
(And MAC address is not written in BIOS; it's in the firmware of each network device itself.)
edit: If you want to monitor whether someone has changed a MAC address after the fact (read: you'll need to have captured the original MAC address first), you can use a utility like arpwatch.