Here you go,
BMW Rocks wrote this:
"The airbag is mounted to the door behind the door panel. You don't have to worry about it if all you have to do to get to the speaker is remove the door panel.
Unless you have to remove it to get to the speaker for some reason. In that case, you would have to disconnect the battery, wait 20 minutes, and remove the air bag and its power connector. This is so the backup airbag power (the bags will work for a short time even if power is lost, a safety feature) can discharge safely. It probably takes less than 20 mins, but that is what BMW calls for. Removing the bags is a bit scary but just be fearless and trust yourself. Just don't power up the car without the bag connected as you will generate fault codes that will light your airbag light, which can only be cleared using a fault clearing tool. Plus you will have to wait another 20 mins to reconnect it after taking the battery cable off again.
I know all this airbag stuff because I had to remove my front door bags to replace the window regulators in my X5."
Here is a link to the whole thread:
http://www.bmwboard.com/forum/showthread.php?t=8113