The Bi-Xenons are basically xenons that are on all the time. A flap/visor comes down during low beam to dim/restrict the bulb. When you turn on the high beams, the flapper retracts and you get full beam = high beam. The other lights (halogen) only come on when there is a problem with the Xenons or when you want to flash and the Xenons aren't warmed up yet. I only know this because I had far too many headlight issues that caused me to know more than I ever wanted.
Bi-Xenon means there is one light on the Left side and one on the Right side. --- (Only Kidding). Bi-Xenon is as cmcreller describes. When the Xenon bulb is on Both the Low Beam and High Beam come from the one bulb but use a shutter as described. When the Xenon bulbs are on there is a relay in the light housing that turns off (deactivates) the Halogen bulb. However if the lights are turned off the Halogen bulb will operate in the Flash to Pass mode, saving the cycling of the Xenon bulbs. There is a way to defeat this relay by disconnecting the realy ground lead (brown) which will allow the Halogen bulbs to light for both Flash to Pass and High Beam when the Xenon bulbs are on. I have made this modification on my Bi-Xenon and when I put the High Beams on it's like daylight for several hundred feet. This modification has been referred to as the Euro-Mod since I think this is how the Bi-Xenons work in Europe.
Mike
Xenons on all the time 
Linear Mode
