Panther install in older (tray loading) G3 iMac?


We have a few older G3 iMacs (tray loading) on our school network that I'm trying to upgrade via disk image. Booting off the firewire drive has proved very quick and effective for our firewire equipped machines. But these tray loading (333mhz) machines have no firewire. One of my drives has a usb connection. Can I boot through usb?
Last alternative is to just load everything from disk. I guess I could spend my summer off just doing that at school......hmph.
The Slot loading iMacs were the first that were able to boot off a USB device.
So I guess that it's a slow go to Panther for those machines....
I do have a couple of slot-loading non-firewire (350mhz) machines that I will try though.
Thanks Bob