I have a 2000 Regal GS, with the supercharged engine, and read this thread because I also couldn't find the radiator drain plug. I finally found it in the location stated above, lower driver side corner toward engine, but mine is black -very hard to see, and when I finally was able to turn it I found it had to be turned multiple revolutions, not just 1/4 turn, and finally coolant started to come out from the small hole in the center of the large rubber grommet directly below the drain plug. Maybe this is a different design from the standard Regal, but that's what I have.
BTW, to get the plug to turn, I found it hard to get a 1/4 drive into the space, so I cut a slot, just wide enough to slip over the wings of the drain plug, in the end of a 3/4" wood dowel that was about 3 inches long, and turned it by hand, worked pretty good.
I joined the forum just so I could respond to this; it looks like a pretty good source of info so I will proabably refer to it often in the future.
