The caveat here is that I have not done this myself yet. This info is taken from several sources. Torques and procedure were confirmed with my Bentley manual.
Those of you who have done this, feel free to jump in with any hints or advice.
PROCEDURE
1. Center steering wheel and make sure front wheels are pointed straight.
2. Disconnect negative cable from battery.
3.***WAIT AT LEAST 1 MINUTE AFTER DISCONNECTING BATTERY BEFORE WORKING ON THE AIRBAG***
FOR SPORT STEERING WHEEL:
4. Insert screwdriver through opening in rear of steering wheel and push against spring tension to release airbag unit lock.
Repeat procedure on other side of steering wheel.
FOR MULTIFUNCTION STEERING WHEEL:
4. Loosen (2) Torx T30 screws behind steering wheel while holding airbag in place.
5. Lift airbag off of wheel and disconnect harness connector.
6. Remove steering wheel center bolt.
7. Confirm steering column and steering wheel match marks (arrow below) and remove.
Store airbag horn side up.
REINSTALL
1. Align steering wheel and column match marks.
2. Align steering wheel to alignment pins on steering column switch block.
3. Reinstall steering wheel center bolt. Torque to 46 ft-lbs.
4. Reinstall airbag. Reconnect electrical harness connector.
5. Torque airbag T30s to 8nm or 71 INCH lbs.
Edit: Another thing you might notice while paying close attention to your steering wheel is that it does not seem to be parallel to your chest/seat while you sit in the car. It might seem that the right side of the wheel is just a little closer to you than the left side of the wheel.
This is because........ the wheel actually is mounted that way. After taking measurements from several e46s on this site, we were able to confirm that the steering wheel is in fact canted slightly with the right side of the wheel approximately 1" closer to the driver than the left side.
It is a small enough distance that you won't really notice it unless you are really looking for it, but if you should notice it, take comfort in the fact that it's completely normal.
For reference, other DIYs:
http://www.bmw330ci.net/projects/m3wheel.php
http://www.my330i.com/mod23.php#D
Also some good info here http://www.zhpmafia.com/forums/showt...by-Wheel/page3