Assuming you have a USB floppy drive, there are command line methods to format floppies
http://forums.macosxhints.com/archive/index.php/t-15882.htmlbut with Tiger 10.4.9 I have been unable to get a reliable 720k floppy suitable for the Amiga [or Atari ST as well]. Maybe Leopard will work better?
I've been using my retro Power Mac 8500 to do this. Maybe you can install OS9 under "Classic" and then format 720K floppies that way, I'm not sure but it seems logical.
let us know if it does work.