I mostly use photoshop, but use psp for flood/spot lights. I take the final texture (.bmp) and
without zooming in put the lights wear I want them, Adjust the size, brightness, etc... Enter, then backstep to remove the lighting from the color map. You actually only want to apply the lights to the light map, not the color map.
Create a blank texture of the same size, medium grey (128 brightness, 0 saturation). Apply the lights to this texture using the "last used" setting. I usually double the intensity and set darkness at 50%, but you can vary that to taste, then enter. Adjust brightness and contrast to get a black background and the light's brightness where you want it and save it. Stick it in as a seperate layer on the psp version of the texture it's for under the other glowy areas on the texture (windows, etc.) but above everything else. Flatten and save either grayscale, the way Taldren did it, or 8bit (256 color) if you want to have colored light maps, for warp glows and stuff, and use as little memory as possible.
I hope this is helpfull. It's a pretty "down and dirty" description, I know.
P.S. I love the shots in space dock.