WIthout these you are up a creek.
So, do you have any idea what operating system this PB G3 is running?

If it is System 9, the one before OS X, then this password thing is probably controlled by a third party piece of software.
Try starting the computer with the SHIFT key held down.

If it is OS X, then you will need the installation disks to reset the password.

10.3 is probably about as high as that machine will comfortably support. Any of the OS X installation disks will do the Password Reset thing, just don't borrow one that is above 10.4 as your computer may not boot from it.

BTW, that user is not still logged on. The computer needs a username and password to allow access to it.

Let us know how you get on.

P