The latest version of XPostFacto has initial support for booting Panther on older Macs:
XPF now includes limited support for Panther (Mac OS X 10.3) on the 7300 – 9600 (and friends), as well as the Wallstreet Powerbooks and Beige G3 (with some limitations related to video). The original Powerbook G3 (Kanga) is not yet supported, but I will be working on it.
Of course we’re still in Alpha release mode, so it may work for you and it may not. I sent in $10 to fund development a few weeks ago, as eventually I should ne able to boot a recent version of OSX on my hopped up G4’d 8500.