first off, look for the one with the reddest comb. If they are all red, flip them over and look for the one with the pinkest, widest, moistest looking vent. If they all look the same, drop food coloring of different colors in each bird's vent. Supposedly it will tint the next egg to be laid and you will know then by the color who is laying what. Good luck, and DO post pics of whatever way you figured out the one laying! Lots of people want to know the answer to that and you can help everybody learn.
Interesting post from Dixiedoodle about the game cam....I've been thinking about a remote cam fed into the computer to check out the ladies.
Also had a thought about doing a complete webcam for one egg from hatching to six weeks of age or so....I wonder if that would be feasable?