Hi, i just tried HORIZON software for first time, i transfered all the maps with it to XBOX360 prepared USB , everything looks ok in horizon, but when i put to XBOX it says corrupted to almost every file. And some were OK, but after copyiing it to xbox HDD i still didnt saw then in the game. So, could you please give any advices hot to get all the MW3 maps to xbox for free? Thanks a lot for helps 
You need an RGH or JTAG’ed xbox in order to get free DLC, not a flashed Xbox. The only DLC you are able to get for free is DRM free DLC.
OK, but for example for MAFIA II it was no problem to burn DLCs to DVD and install it to HDD as addon, is no such thing for MW? Thanks
Mafia II DLC was DRM free, allowing it to be added by way of flash drive, or by burning to disc and installing it. Unfortunately there’s only a small amount of content that’s DRM free, and addable, and playable on stock or flashed 360s. I’ll leave a few links below that will show you all DRM free content available as of now.
DRM free thread: https://www.horizonmb.com/threads/153849-aden34-s-DRM-Free-Thread-NEW-LINKS!-%28Bioshock-Infinite%29?highlight=aden34
Another DRM free source: http://www.zippyshare.com/kill_seth
Anything found at those links can easily be added with Horizon & a flash drive, no need to burn a disc.