Photoshop :: Color Seperation

I'm Having problems with seperating the color chanels in PS7 on a grey scale image.

I have 3 pcitures and want to extract 1 color chanel from each and then combine them. Here's a section a an email I have describing the the procedure. However, I'm still at a loss.

When using Photoshop, there are two methods of controlling the color
level in a frame as I remember, and one of them will result in improper
color balance.

When you independently adjust the color level, one of the methods (and I
don't remember which) will leave a frame that ranges from black to white
with the pure color as the only tint. This is the wrong method, as a pure
color frame cannot possibly have white in it. The method you want will run
from pure black to pure color (such as green) with no gray or white
whatsoever. You can test the method by looking at the RGB frames
individually. If you are trying to get a red frame but the RGB
decomposition reveals any green or blue information at all, then it is
incorrect. The green and blue frames in a pure red image should have a
completely black image.

Now, when you have your pure red, green, and blue image data, to
assemble them you know that each must contribute 1/3 to the image. If you
assemble two frames at a time, the first two must use 50% transparency so
each contributes equally. The next assembly must use 67% transparency so
that the first two frames account for 2/3 of the image data, the next
accounts for 1/3. As you can see, the order of assembly here will have no
effect on the process. That proves that the process is as it should be.

Once the frames are together, the overall image will be about 1/3 as
bright as it should, so the brightness and contrast must be increased by
roughly 2/3. Compare them to a straight assembly of the calibration target
to see how it should look.