He says it is available through XBLA for 400 points or $5 o something like that. I agreed to give him the gift code if it turns out he can redeem it for the Xbox version.
Your title says "have beta gift code" - Minecraft is no longer in beta. There will be no beta versions on XBLA, afaik
Therefore a "beta code" would not work on Xbox 360 as the versions on Xbox 360 are not beta versions
Are you talking about a beta code for the PC version of Minecraft? If so, it will only work for the PC version of Minecraft (will not work on Xbox 360) [ Source: http://www.minecraftforum.net/topic/840271-minecraft-xbox360-information/#14 ]
Secondly, Minecraft is not out yet for Xbox 360. When it comes out, it is estimated to cost 1,200 MS points ($15). 400 points would be extremely cheap for this game, and I seriously doubt they would sell it for that price. In fact, I am absolutely sure they wouldn't sell it for that price
Are you sure your friend isn't talking about Total Miner or CastleMiner currently available on XBLA? They are 240 MS points ($3)