where is the video stored ??????
i hope you do not even try to connect a external harddrive via usb to it , as the iMac g3 only gas usb 1.1 which is far to slow to to get a video from a external harddrive , if you use a external harddrive then connect it via firewire and that problem is solved
you can even get the video via apple talk if you have connected your iMac via ethernet on your router from your other mac then you will be able to play video ,
of course do not consider hd video playable , hd was not even invented back then
and dont use flashplayer 10 for the g3 , as flashplayer 10 needs at least a g4 processor to even be considered as working at all