I'm not sure if CS2 has this, but before you go to grayscale, go to Image/Adjustments/Black & White. There, you can adjust the lightness and darkness of the grays that will result from each color in the image; move the sliders around and it should be pretty obvious what you can do with it; say a red in the image is coming out black when going to grayscale, move the red slider to the right and it will be lighter. Check it out, if it's available in CS2. If not, then yes, go your other route. You could also alter the R,G or B channels separately in the levels or curves box, lots of options. But if you have the Black and White function, go there first...
Steve