All you do is take a pokemon you want to duplicate and make sure it's holding a Masterball, to save pressure. Go to a pc, and switch to a box you haven't used yet. Save. Deposit the pokemon you want to duplicate in the empty box. Switch back to the box you were on before. IMPORTANT! When the save box says "Saving. Don't turn off the po...", TURN THE GAME OFF! Then turn it on. You should be in front of the pc with the pokemon in your box and in your party. (You should check out for the few tips and hints I've laid so far on Pokemon Sappire if you have it, it might help a little... ^_^)

Yes, you can catch Ho-Oh in Crystal