Carcassonne

[Richmond]

I am playing around with tiling games, mainly as I use Carcassonne 
extensively as a teaching aid in my ESL school.

I have got to the, admittedly fairly primitive stage, of making a set of 
tiles, each capable of being dragged and dropped onto
a grid consisting of drop-targets made up of rectangular graphics.

Each of these tiles also "owns" a button in its centre that allows it to 
be rotated.

HOWEVER I have 2 main problems:

1. How do I make sure that once one of my tiles is 'occupying' a drop 
target no other tiles can be dropped on it?

2. How do I make sure that a tile can be dropped on a target ONLY when 
its sides match the sides of adjacent tiles?

Pictures and stack here:

http://forums.livecode.com/viewtopic.php?f=22&t=25965

Richmond.