You forgot your username and password to get into your Macbook and you don't have the original CD?
You can use this tip to create a new administrator account - then you can change the other passwords. Make sure you don't add space in between the db/.Apple and use capital letters where they sit in the code and it should work:
# Press Apple + s down after you hear the chime.
# When you're prompted to do so, enter these commands to create a new administrator account (hitting return after each line):
mount -uw /
shutdown -h now
# After rebooting you should have a new administrator account. When you login as the new administrator you can delete the old one and you're good to go again!