Solipso
Chieftain
I apologize if this information has been previously posted. I tried a few searches, but got no relevant hits. 
What follows is my easy step-by-step procedure for allowing you to listen to the Civ IV theme song while you are at the Civ IV BTS main game menu.
Note: Unless you are playing the Sid Meier's Civilization IV The Complete Edition, your paths to the two Soundtrack folders that you need to open WILL NOT BE THE SAME AS MINE. That is, you will not have any folder "Sid Meier's Civilization 4 Complete." I suspect you'll just need to go to "Sid Meier's Civilization 4," but I don't know. Also, I think that if you're using Window XP, or earlier, you'll need to go to "Program Files," as opposed to "Program Files(x86)." Nevertheless, if you take a look at the paths that I provide to the two Soundtrack folders, I believe you will be able to figure out on your own what the exact path is that you need to follow.
Here is my procedure:
1. Go to C:/ProgramFiles(x86)/2K Games/Firaxis Games/Sid Meier's Civilization 4 Complete/Beyond the Sword/Assets/Sounds/Soundtrack
2. Open the Soundtrack file
3. Copy/paste the OpeningMenu file to a new folder of your own creation. This OpeningMenu file is the BTS theme song that you hear at BTS's opening menu. You should also save this OpeninMenu file to a backup drive. Then if you're tired of listening to the Civ IV theme and want to listen to the Civ IV BTS theme, you can recover the BTS theme and copy/paste to this Soundtrack folder.
4. Having saved the OpeningMenu folder, now delete it.
5. Go to C:/ProgramFiles(x86)/2K Games/Firaxis Games/Sid Meier's Civilization 4 Complete/Assets/Sounds/Soundtrack
6. From this Civ IV Soundtrack folder, copy/paste the OpeningMenu file to the Civ IV BTS Soundtrack file that you previously opening.
7. You should now hear the Civ IV theme while playing Civ IV BTS.


What follows is my easy step-by-step procedure for allowing you to listen to the Civ IV theme song while you are at the Civ IV BTS main game menu.
Note: Unless you are playing the Sid Meier's Civilization IV The Complete Edition, your paths to the two Soundtrack folders that you need to open WILL NOT BE THE SAME AS MINE. That is, you will not have any folder "Sid Meier's Civilization 4 Complete." I suspect you'll just need to go to "Sid Meier's Civilization 4," but I don't know. Also, I think that if you're using Window XP, or earlier, you'll need to go to "Program Files," as opposed to "Program Files(x86)." Nevertheless, if you take a look at the paths that I provide to the two Soundtrack folders, I believe you will be able to figure out on your own what the exact path is that you need to follow.
Here is my procedure:
1. Go to C:/ProgramFiles(x86)/2K Games/Firaxis Games/Sid Meier's Civilization 4 Complete/Beyond the Sword/Assets/Sounds/Soundtrack
2. Open the Soundtrack file
3. Copy/paste the OpeningMenu file to a new folder of your own creation. This OpeningMenu file is the BTS theme song that you hear at BTS's opening menu. You should also save this OpeninMenu file to a backup drive. Then if you're tired of listening to the Civ IV theme and want to listen to the Civ IV BTS theme, you can recover the BTS theme and copy/paste to this Soundtrack folder.
4. Having saved the OpeningMenu folder, now delete it.
5. Go to C:/ProgramFiles(x86)/2K Games/Firaxis Games/Sid Meier's Civilization 4 Complete/Assets/Sounds/Soundtrack
6. From this Civ IV Soundtrack folder, copy/paste the OpeningMenu file to the Civ IV BTS Soundtrack file that you previously opening.
7. You should now hear the Civ IV theme while playing Civ IV BTS.


