There's an interesting discussion underway at the RepRap forums, where the idea of Direct Metal Laser Sintering is being pondered. DMLS involves laser-heating metal (or other material) powder, layer by layer, slowly building up a solid object. This is pretty similar to how many 3D printers work, but the interesting bit is that these guys are contemplating designing a system that could do this at home:
In other words, it's a laser cutter with a powder bed. This should be hackable by combining an off-the-shelf laser cutter with Fab@home or even CandyFab technology. From there it's all about finding the right settings.
It may be necessary to work under a nitrogen or carbon dioxide atmosphere, as steel powder is highly flammable under the right conditions