Most Bmw wheels are compatible with the X5!The problem is that the X5 has a different OFFSET(ET).This determines wheather your wheels stick out of the bodywork,are level or go inwards.
Wheather a another Bmw wheel still fits ok on the X5,depends very much on the size of the wheel!To give you an example,we have a member here riding on 7-series wheels(19"s I think)but these stick out a bit!This is because the 7-series offset is smaller than the X5's!
If you know exactly which Bmw wheel you want,I can advice you further!