How do I set the same password for both initial login to the Macbook Pro , How do I set the same password for both initial login to the Macbook Pro

Currently using a Macbook Pro ( OS Lion) on a windows based network.

Due to network security a user must change their password once every 3 months.

This results in the user having to remember 2 different passwords as the network password is different from the password used when the Macbook powers up initially.

How can the same password be used for both?