OG = original generation.
But yeah get an original xbox if you can -- most of the games dumped for the original xbox will not work with a basic DVD flashed 360 (they work fine for the original xbox, however the 360 upped the security checks a bit). You can do more with a JTAG/RGH type 360 hack but you also run into the issue that the 360 backwards compatibility is not all that great.
Equally current DVD flashing techniques are even more annoying, if they even work at all, to use with copied original xbox games.
Also if you do get an original xbox get some component cables and a copy of enigmah video switcher after you have hacked it (assuming your flag is accurate and you are in Poland/PAL country).