Oh dear. I would bet money on you having blown head gasket.
As a crude check, start it from cold, allow it to warm up for no more than a minute, then have someone compress the radiator top hose with their hand. Rev the engine hard. If the compressed hose becomes pressurised, you definitely have a blown gasket.
You need to fix it ASAP - diesels do not respond well to overheating, and in addition to the gasket you will need to have the head crack tested and skimmed.
Phil Saunders
April 2009