The BMW Style 99 wheel listed is listed as the "winter" wheel for the e53 4.8is and it is an 8x18 w/40mm offset wheel. I'm sure that the e53's Style 131 wheel that is 8.5x18 w/48mm offset shouldn't present an issue.
The extra 1/2" width and 8mm offset difference falls within range of the e53 wheel's specs. You should also see that 18" winter tire sizes are listed on your drivers' door jamb tire pressure chart and in the owners manual.