Digital BW, The Print

I'm starting with an RGB full color image and I want to convert it 
to black and white and print after loading Roarke's  UT2 curves.  If 
I just desaturate the color to get a black and white image, there's 
still information in each color channel which seems to screw up the 
curves (when I load them and print I get a useless image, ie few 
grays, heavy black, white, etc).  I can solve this problem by going 
to image ->convert to grayscale and then image-> convert to RGB and 
then loading the curves. But I understand that I'm losing image data 
by converting back and forth between RGB and grayscale images.  
What's the best way to convert to grayscale if I'm starting with 
with a color RGB image and want to print a black and white image in 
RGB mode using UT2 curves?

Great Thanks, Jonathan