Did this yesterday. Drained 4 qts and took 4.5 to fill it back up @ 127k.
What surprised me the most was the fluid that came out was just a slightly darker red than new fluid. I drive ~650 miles a week, most being on the interstate with a few stops and go's when I hit a major city.
One note, I didn't use jack stands to hold my car up. Just had all kinds of heebie jeebies about getting under a running car on jack stands. I built 4 cribbing stands and jacked the car up in stages and put them under the wheels. Gave me a good 20 to 22 inches of clearance under the car.
Here's the link of the design I used. Though I added chocks on the top section.
http://www.myturbodiesel.com/wiki/wo...o-jack-stands/
Also, due to the way BMW suspensions work you need to watch how the suspension "spreads" as the car is lowered down on to the cribs. I had to jack the car back up, slide the top section over 1/4 to 1/2 inch and then lower it back down to make sure they were square standing.