The clouds are being moved with a simple animated position value. This is pretty easy with jQuery if you want to keep it simple as possible. The trick being looping the effect. Check out this tutorial that cropped up on J4D recently. It shows you technique to achieve the effect your after. Possibly?
thanks for the response Toby but it doesnt really help. I cant get anywhere with that tutorial. I have sort of achieved this look before using the horizontal way template. I need it to move on its own like in the site mentioned. Sorry to be a pain.