1. go to steam/steamapps/common/modern warfare 2 and copy the modern warfare 2 folder..
2.now just go to my documents and paste
3. now add the ALterIWNet thing to the modern warfare 2 folder u have in my documents..
4. now ur steam/steamapps/common/modern warfare 2 stays the same now u wont get banned!
5. and when u wanna play the AlterIWNet server just go to my documents and double click the modern warfare 2 folder and just click iw4mp.exe =D