Couple of things here.
To swap over you don't only need the xenon housing. You will also need to purchase a conversion harness that gets rid of the error that comes up when doing the swap.
You will find a lot of information on e90post.com:
Search "Halogen to Xenon", there is a member named E90 Andy there that sells everything you need to do the swap. His latest work actually eliminates the conversion harness making it a lot easier to do and more OEM. I am in the process of changing out my halogens to xenons.