Random Motion problem

Hi,

I had a look at your tutorial with regards to the Random Motion. The script works fine but there is one problem that I need to solve. If I create a canvas larger than the movie height and width, the movie will still go back to its original set coordinates in the the left hand corner. How can i set this script so that the movie only plays at a certain part of the canvas. This is quite urgent, so I would appreciate a prompt reply

Thanks

Jaison