2.0TDI?
Something similar just happened to my mate, the tensioner stud pulled out the head so the cambelt came off, he was doing about 40mph.
He was very lucky, because of the design of the head/valves etc the pistons smashed the valves up and it just snapped all the rockers. Every valve is sweet as is the head, he just fitted new rockers and a new belt.
Like Hurdy said though if the engine isn't moving at all it sounds a bit more terminal :(