Are you going to carry a car battery too? Forget the 80W car HID idea. It's totally overkill. The 10W bicycle HID are bordering on too bright as it is. If you want to DIY one, look at the Trail Tech kits directly from Trail Tech and build your own battery. It would be advised to do a search on Battery Space in the forums before doing business with them.

http://trailtech.net/lights.html