swaping in a diesel engine into a gas VW

[GasSavers_Ryland]

last weekend I talked to a guy who swaped a Diesel engine in to his gas VW Rabbit, as he explaned it was extreamly simple, as the Diesel engine only uses a fraction of the wires, has a mecanical engine mounted fuel pump, and I belive he said it bolted right in, of course you need a transmition from the diesel as well for the proper gearing (unless you want to use it as a tractor), so I got to wondering, how hard is it to swap in a newer diesel engine in to say a VW gulf? I know that once you get in to things like the new TDI VW's that things get extreamly complecated due to them being a drive by wire system, but how about those older TDI engines? or just the normal turbo diesel vw engines, I think it's worth thinking about, espsialy if you drive distances, and are having truble finding a small diesel car, junk yards seem to want $250-800 for an engine.