The PowerMac G4 you won is a great machine! It does not appear that OS 9 is installed on it...the seller said they had 10.5 Leopard on it, so that does not support Classic...
In any event, if you can find a version of ClarisWorks or AppleWorks, it will run in OS X (I think you need version 6).
If you can find the older install disks, you can put an older OS (like 10.4) on it that will support Classic...
For software, you should look at (google) Macintosh Garden.
You can also look at scooping up other old bargains, that include software or install disks, and use them on this machine as well.
I also meant to say, you should google the user group for the old WordPerfect program. They are on Yahoo! Groups. They have a Sheepshaver boot disk that is quite helpful. I have always found Sheepshaver to be tempermental on my Mac's...it works better for me in Windows, for some reason.