You have to be very careful when removing a case, not only to protect the card, but to not hurt yourself. The cases are called "slabs" for a reason. I used big wire cutters, a very sturdy screwdriver, and a hammer to help wedge the screwdriver into a seam. Take your time and wear goggles in case some of the plastic pieces go flying. It took me close to half an hour to remove the case.
Blimey Cindy, there's a reason we call you supermum... and that's because you'll take a hammer and a chisel to anything if it means your cards are kept nicely!
Welcome Chris, I personally would like to add that (though I love Artbox as much as you all!) Artbox's HP cards have always suffered in the packing process and I must say that very often the cards are not mint. If you get 'into grading' you might get into the numbers they attach to them and really struggle to get the high numbers you seek...
Just a thought though - do what your heart tells you ;o)