Scud,
This is propably the one you are refering to:
http://e46fanatics.com/faq/stereosaga.html
I followed this one last weekend as I have a Ci, the door removal part went well.
http://www.bmw330ci.com/DIY_Door_Panel_Removal.htm
Are you just adding the mb quarts to the existing system, or do you have an after market head unit and amp. If stock you will run in to a couple of annoying issues.
1. Cross-overs internal to the amplifier to three separates (tweet, mid and woofer) instead of two.
2. 2 ohm woofer, 8 ohm mid & tweet.
I think I solved the two above item, but I am waiting for some 4 ohm power resistors to come in to verify.
Fortunately I have a good friend that did custom car stereo installs for about 10 years in southern california and is an electrical engineer to boot.
SAB30