If you can find the pages on headliner removal then you're halfway there. Once the headliner is out you can unscrew the rails from the roof. It's pretty straightforward. They're not only mounted with screws but there's also a rubber strip sealing and four (not so flexible) tubes for draining water.
Could be a good opportunity to take care of that sagging headliner if you have one.
ETA: there you go
http://www.wlsheadliners.com/tutorials/bmw/
Last edited by Morgenster; 07-28-2008 at 10:05 AM.
2008 audi A3 1.9tdi
(former 1991 520i LPG)