1.) Make sure it will work in your Xbox 360's region!

Region Free Will work on any xbox360
NTSC/U used in America, Canada, Mexico
NTSC/J used in Japan and Asia
PAL is used in Europe, Australia, and Africa

2.) Can I play Wave 4 and Wave 6 games?

IF you are on iXtreme 1.5 or below,
Wave3 games will not boot for you and thus Wave4 games will not either. In this case, YES you need to update your firmware!

IF you are on iXtreme 1.51 (Hitachi),
then ANY wave will boot fine, including Wave4 however you must be EXTRA careful as you are not protected against corrupt or incorrect video partitions.If a game is fully verified, playing it on iXtreme 1.51 is just as safe as playing it on iXtreme 1.6 - this includes Wave4 games.

IF you are on iXtreme 1.51 (BenQ/LiteOn/Samsung), then YES you need to update your firmware! Wave 4 will not work!

IF you are on iXtreme 1.6,
you can ALSO play Wave 4 and above games, however you need to use a special activation disk to do so. This was added to the firmware specifically for this eventuality - the disk activates "one-shot-boot" mode, essentially it allows iX1.6 to boot any game you insert into the drive, even if its not properly stealthed. You simply insert the disk into the drive, let it spin up (it will say "play DVD"), then swap in your Wave4 game. You will need to do this each time you want to play a Wave 4 (or above) game. Don't worry, if the game has all the necessary stealth data, then iX1.6 will still use it, so if you boot a VERIFIED Wave4 game using this method, you should be just as safe as you were booting a verified wave 3 game.

IF you are on iXtreme 1.61 or iXtreme LT you are fine and you can play Wave 4 games AND WAVE 6 GAMES without an activation disk.