[Daemonblitz]

If the 19s work i don't see any reason why the 18s would not. They are still the same width and offset.

F: 8.5" wide ET:29
R: 9.5" wide ET:23


As for weight BMWs "claimed" numbers, the 18s are:
F: 11.05 kg (24.36 lbs)
R: 11.75 kg (25.90 lbs)

The 19s claimed weight:
F: 10.7 kg (23.59 lbs)
R: 11.4 kg (25.13 lbs)

As a point of reference our stock rims claimed weight for cars built until 12/07:
F: 12.15 kg (26.79 lbs)
R: 13.65 kg (30.09 lbs)

Cars built after 12/07:
F: 12.0 kg (26.46 lbs)
R: 13.3 kg (29.32 lbs)

Again, these are the "official" numbers according to BMW, and real life weight might be slightly different, but it still gives you a good reference.