dq to the rescue....
here you are a pic of the suspicious subject
the rivets
and the assembly
as it has been said, first remove door card to have access to the hexagonal bolt that holds the lower part of the window frame and likns it to the mechanism
be aware that the mechanism has a plate that holds the thing in place, and that you will have to slightly undo a small phillips headed screw, check it in post #22 of the same thread:
http://www.e9coupe.com/forum/showthread.php?t=13485&page=3
it is critical, do not hesitate to ask questions, you will see two holes to access this bolts, one is big for the hexagonal bolt, abd the other small, for the phillips headed bolt, be careful
once the bolts are undone, drill out the two rivets on the top, and then the triang window is free to pop out, you will need to bend and force a bit do not worry
remark, i found almost impossible to remove the glass from the chromed trip, it is glued !
good luck
remark, get the mechanisms from the parts car too, the are highly NLA !