I've thought about doing the same thing (installing projector fog/driving lights) but don't want to make it TOO much of a hack job. I think it would look "odd" to install these in the original housings, and having an extra (old, scratched) layer of plastic lens in front of the projectors isn't going to help anything, either.
My thought was to fabricate a flat black panel that replaces the original fog lights, that projectors could be bolted to. It's just waaaaay too far down on the to-do list for me to think it's ever going to happen. I've made do by installing brighter (halogen) low-beam bulbs, which made a big difference in the light output. I don't think much about the fog lights, because it's pretty much impossible to tell if they're on or not... ;-)
My thought was to fabricate a flat black panel that replaces the original fog lights, that projectors could be bolted to. It's just waaaaay too far down on the to-do list for me to think it's ever going to happen. I've made do by installing brighter (halogen) low-beam bulbs, which made a big difference in the light output. I don't think much about the fog lights, because it's pretty much impossible to tell if they're on or not... ;-)