I'm gonna have to put in my 0.02 here and disagree with some of the statements on this thread.
Although I agree that MOST cars can't handle an HID bulb in their halogen housings, the 4th gen 4Runner is not one of them. The 4R is a PERFECT candidate for the HID system. There is absolutely no glare produced, and the cut-off is as sharp as the halogen's. I have HID's in my 4th gen since the first day I brought the car home. 1800 miles later, NOBODY has flashed me... EVER. This was on city highway combined driving mostly at night.
(I just got the truck two weeks ago and racked up the miles by driving to Canada, I like driving at night.)
Additionally, I own a G35 coupe with factory HID's and my buddy has one too, but his is stripped down with halogens... our reflector housings are EXACTLY the same.
Also, we tried installing a set of HID's in my friend's '03 Tundra and the glare was horrific.
It depends on the car. But the 4th gen is definetely good for it. If you're real picky you can aim the housings down a little, but IMHO, it isn't needed. It's a simple plug and play.
Flame suit on.......