I hope you have a second HD or partition with OS 9.2.1 on it. A beige G3 with that processor would be a screaming OS 9 system, the 768MB RAM ceiling just makes it a limited OSX machine (along with PCI video).

What happened to the original PS anyway? You can use the Mac supply or ATX just by moving a motherboard jumper but I never seen a reason (power draw) to bother using a beefier ATX one in mine.