If you have a JTAG machine later versions of iso2god (and some standalone programs like xbe2god if the name has not escaped me) added support for original xbox isos. Not sure about standalone/extracted iso playback. Bonus with JTAG is you can use the hacked emulators to do nice things.
Without a JTAG machine you are out of luck. You can burn the isos using those convoluted methods if you have a flashed drive but otherwise you are getting the original game.
Frankly original xbox and 360 games are always a pain to get sorted (be it stock, flashed DVD or JTAG) and original xboxes are not hard to come by and flash (indeed you can do it with nothing more than a IDE/pata port) so I tend to suggest that.
If you are messing with something other than JTAG then you need the complete iso- many scene releases of the original xbox era had parts ripped for size purposes and are totally unsuitable as a result.