Hi, and Welcome to the forums!
Yes, below I will provide some links so you too can learn how to boot a PowerPC mac off of USB.
http://hints.macworld.com/article.php?story=20060301112336384
http://hints.macworld.com/article.php?story=20101011105729488
http://blog.campodoro.org/?p=43
Of course.. your milage will vary... To sum this all up... You would need to go into Open Firmware by holding down: Option+Command+O+F. Once in OF, you need to type devalias. This will list your hardware devices connected and installed inside your Power Mac.
Next look for "ud"... ud means: USB DEVICE... Once you find ud, then type the following.. make sure your USB device is in place.
boot ud:,\\:tbxi - This will boot Mac OS X or any bootable OS X disc, providing it works with PowerPC. You can also use this to load Diskwarrior or other applications which have a Mac OS X System folder.