Try Bavarian Autosport (
www.bavarianautosport.com). There you can input your year and model BMW and shop through all parts and accessories which apply to your car. Under 'Exterior' and then 'Lighting' you will find 'High Output Upgrades'.
Bavarian Autosport sells a true-Xenon/HID system apparently applicable to your car. It costs $899.95, and includes all components and instructions necessary for what they claim is a relatively simple switching procedure you can do yourself. As for the price, it seems about right for a genuine HID kit.
If you prefer not to spend so much money on such a conversion, you may want to consider PIAA SuperWhite 9005 (high beam) and 9006 (low beam) bulbs, which Bavarian also sells. These should be a direct swap for your current bulbs. They cost $74.95 for each pair, so you're looking at spending about $150 to bring your headlight illumination very close to HID levels (although this is
not a true HID system.
As for the 1999 7-Series, I was under the impression that HID lighting was standard by this time. At any rate, Bavarian Autosport does not appear to have a conversion kit available for a 1999.
Good luck to both of you. I upgraded the headlights of my own '86 528e (H1/H4 bulbs) with Hella Quartz Halogen lights (not applicable for newer cars), and found the difference quite dramatic, so I'm sure your efforts will definitely be rewarded!
Craig