http://www.deliaonline.com/cookery-school/how- to/how-to-dress-a-crab,66,AR.html
Part One:
How to dress a crab
1. The first thing to do is choose and buy your cooked crab. The fishmonger will pull it slightly open so that you can see it's full of meat and not empty. Back in your kitchen you'll need a chopping board, two bowls (one for the white meat and one for the dark meat), a small sharp knife, a teaspoon, a metal skewer (preferably flat), and either a small hammer or a pair of nutcrackers.
2. Put the crab on its back on the chopping board, so that the claws and softer body section face upwards, then simply twist off the legs and claws � they'll come away very easily � and put them to one side.
3. Now put your thumbs against the hard shell close to the crab's tail, and push and prise the body section out and away from the shell.
4. From the shell remove and discard the small greyish-white stomach sac, situated just behind the mouth.
5. Remove the long white pointed 'dead man's fingers' from the body section. These can be easily distinguished and it is a quick and easy job to remove them.