I have installed several versions of Oracle on Windows platform several times, and it had always asked me to provide password for the DBA accounts during the install. There is probably no default password on any platform, you had to provide one when installing. So no luck there. If it is of any help, the initial users you use to manage the database are sys and system, and you should do most things as system.
If you resign on reviving the old database, you don't need to reinstall the software. You can simply create a new database using Database Configuration Assistant and forget about the old one. You cannot remove the old one using Database Configuration Assistant, as you would need to know the password. If you didn't put much data into it, it will simply sit there using a few MB of space. Try to enter a password you'll remember this time around. However, 9i is quite dated, so you might want to use this occasion to move on to 11g.
(Famous Oracle credentials for the sample schema are scott/tiger. However, this account is by default locked after installation and does not have DBA access, so you cannot actually do much useful things with it.)