What do you mean to say, that you lost the root password? That you lost all your passwords? More information about the username and password you need (and why you think you need them) would be useful.
If you don't remember the passwords you entered when you installed the system, then you will need to use a boot disk of some kind to change them. The passwords are stored encrypted in the /etc/shadow file. Just clear out everything between the first and second colon, then it will let you log in without a password. Just make sure the first thing you do when you log back in is to change the password with the passwd command.
Post back here if you need more information than that.