Generate random X Y Coordinates within a square/rectangle

Hi,

I'm a computer programmer and am currently coding up an algorithm. As part of the algorithm I need to take a unique ID (either a series of characters or most likely a large integer) and generate an X,Y pair from this ID within a given square/rectangle (I know the co-ordinates of each 4 boundary coordinates of the square/rectangle). These generated X,Y coordinates need to be uniformly distributed within the area and also unique so that every time I do this conversion on a particular ID I always get the same resulting X,Y pair and a conversion on any other ID does not result in the same X,Y pair.

Can anyone help me with how to approach this?

Thanks in advance.