Here's a link to YouTube explaining it.

Here's a link to the console mods wiki for all the details and further mods.

Here's a link for if you're on Linux and can't her bad builder to work (like me) or just lazy (like me) where it's all premade and ready, you just drag and drop it into the flash drive.

Here's a link to where you can get all the games you need. You aren't limited to the approved list for original Xbox.

Here's a link to the software that turns them from ISO to Game On Demand (GOD) files so you can play them right off the console.

You can also games from the flash drive to the internal HDD and even bump it up to a terabyte but I'm stiff figuring that out. Just don't launch them while connected to Xbox live. As far as I can tell there's no harm done during the process but connecting to live while hacked or trying to play games added with the hack can get you banned. Not that I expect anyone is still using live on a console two generations past.

Have fun, be safe, don't die!