trying to summon OSX on G4

I have a G4 400mhz that I gave to a friend of my son's who didn't have a computer. It was running an early OSX. Somehow he had gotten into OS9 and now when I try to start up, I only get as far as the smiley computer logo (OS9) and it won't proceed beyond that. I've been looking for my old installation cds for X with no luck yet-- but it seems even simpler than that. I tried holding down the X key during startup to no avail. Any ideas?
Thanks in advance for your time.