Easy method:

Things you will need:

- brain.exe

- a song

 

1. Open up your m2demo folder (should be in your Modern Warfare 2 folder or in your %localappdata%\IW4M folder.

 

2. In your m2demo folder, create a folder called sound. Create another folder in that sound folder and call it music.

Should look like this: ...\m2demo\sound\music

 

3. Change the name of your song to hz_boneyard_intro_LR_1. Check if it's MP3. If it's not, then convert it to MP3.

 

4. Copy your song to the music folder (...\m2demo\sound\music\hz_boneyard_intro_LR_1.mp3).

 

5. Launch IW4M and listen to your new menu music!

 

_____________________________________________________________________________________

 

Complicated method:

Things you will need:

- brain.exe

- a song

 

1. Create a folder called sound. Create another folder in that sound folder and call it music.

Should look like this: ...\sound\music

 

2. Change the name of your song to hz_boneyard_intro_LR_1. Check if it's MP3. If it's not, then convert it to MP3.

 

3. Copy your song to the music folder (...\sound\music\hz_boneyard_intro_LR_1.mp3).

 

4. Pack your sound folder into a ZIP file (...\RANDOMNAME.zip\sound\music\...)

 

5. Change the name of the ZIP file, it should start with z_ (like z_menusound) and change the ending to .iwd.

 

6. Copy your .iwd file to your Modern Warfare 2\main\ folder.

 

7. Launch IW4M and listen to your new menu music!

 

#updated

 

Thanks for Paulofonta for reminding of that m2demo 'trick', almost forgot that.