Blend the biscuites in a blender to get it all sandy looking. Melt the margarine and then take off the stove, add the sandy biscuites into the melter margarine. Mix. You should get a wet-sand look that can stick together.
Take a cake tray. Line it with aluminuim foil (bottom and sides). Make sure that there is aluminion hanging out of the tray too because you'll use that later to take the cake out of the tray (if you don't have that lach that opens it).
Add the sandy biscutes in the tray and flatten it evenly. You can use the bottom flat end of a wine glass to do this more easily. Put tray into the fridge.
After 15mins of the biscuite in the fridge, start making the Panna Cotta according to the instructions of the box or from scratch. You don't want to start straight away because the biscuites won't be cold enough to put the panna cotta over.
Put the panna cotta as a thick layer ontop of the biscute layer. Back into the fridge for a few hours.
Take it out of the frigde, then out of the tray by lifting it out via the aluminium foil. Take the aluminiom foil of and out slowly.Make sure you put it on what you want to serve it on straight away when you take it out of the tray. It's not hard to pull the aluminium out from under it. Ask someone to help you so the crust doesn't break.
Spread a thin layer of jam or fruite sauce or something similar (if you didn't get it in the box of panna cotta) ontop. Then add the melted fruites/berries or fresh one's.Serve :D