Carol, I use Pocket Stars on my PDA (Dell Axim) and Cartes du Ciel on my laptop to give me the coordinates that I need to find stuff. CdC is free but Pocket Stars is $19. CdC shows the comets and lets you update the database. Pocket Stars does not show comets but if I look up the comets on CdC then I can pick it out from the Pocket Stars.

The PDA is definately easier to use out in the field than the laptop.