I normally won't resurrect an 'antique' thread, but want to chime in with my personal experience, as I've seen, in my opinion, a lot of misinformation regarding HID's in older cars. *Warning: Depending on your locale, you may/may not have issues with the authorities if you retrofit HID's into older vehicles. If you do it right and get housings that are designed for them and keep the bulb-color in the 'white' spectrum (6000K or so), you shouldn't have any issues. (I went with 8000K, slightly blue to match the car, and have had no issues at all in over a year).
I don't have any hard/fast scientific data, but my real-world experience has been as follows (this with a tested and verified perfectly operating electrical system): At idle, with stock halogen-type bulbs, when I turned my headlights on, my idle slowed noticeably, and the light output was dim (and bordering on orange in color) until engine speed was increased. After my HID's were installed (using a housing kit intended for HID's and a 35 watt Hi/Lo kit), idle speed doesn't change at all, even during the 10-30 sec 'warm up' period, and the light output is steady across the board.
HID's function in the same manner as a household fluorescent, in that a low-amperage current is fed to the ballast, which then amplifies it and feeds the higher current to the bulbs. Their draw is less than a halogen, and in theory, safer than a stock replacement to your wiring (the harness plugs into one of the stock headlight plugs). And the whiteness of the light output is awesome compared to the yellow that a halogen produces.
My absolute favorite upgrade to date, after the hardened exhaust valve seats. lol

Ymmv...but I highly doubt it.
