Aftermarket parts?

Please forgive me for posting this right here; i am sure there are many threads talking about this particular subject but just navigating to this area was hard enough. Had to get my son to do most of the searching.

I have just bought a very tidy E39 525i. I would like to upgrade the headlights, maybe to xenon halo's. I'm a bit worried about which sites would be the most reputable to buy from and which brands?

Would there need to be any modifications made to the car to accept such aftermarket parts? I'd prefer something that just replaces the original part.

Any help in this regard would be much appreciated.

Thanks

Well, most people here will thell you to search, but in the spirit of the new year, here are a few links to sites you can trust, and I have found through personal experience, are very good...

http://jlevistreetwerks.com/
http://ddmtuning.com/
http://www.bimmian.com/
http://www.turnermotorsport.com/
http://www.bavauto.com/
http://www.modbargains.com/

There are others, but these are the sites I order from...

thank-you; these will do nicely :-)