Without knowing what the wattage difference is between the incandescent(?) you are replacing and the Halogens, it's hard to say. I think it's safe to say that the Halogens will draw more current, how much I didn't find in my quick search. There are other factors to be considered wire gage, and lenght of wire. Here is an article from Hiperformance Chevy;

http://www.chevyhiperformance.com/howto/4417/index.html

The article has some good thinking behind it. There have also been some posts on using Bosch relays here. I'd do a search for them. IF you are also going to be adding some fog lights or driving lights it would be good to learn how to use the relays. It might also be a good time to check what your total current draw is, and if you might be exceeding the amperage on your alternator. I found this listing in my search, the numbers look a little high but,,,, - Typical current draw;

http://townsendsautomotive.com/shared/content/Library/encyclopedia/ch11/11fig16.html

When I was rallying some of the competitors had enough candle power that with all the lights on they were slowly draining the battery, and that was with a 95 amp alternator.

Larry

I don't own a vehicle that isn't old enough to drink.