Nice work Spomenko, I like your decapper. I don’t completely understand how the light bulbs are being applied though. Sounds like maybe they’re being used as a current limiting device. I'm also not clear what you're using for a power source: AC line voltage or a DC source like a 12V battery?
TommyT, if you put enough current through any metal it will get hot. All metals have some resistance, even copper. The amount of heat a metal will generate is given by P = I*I*R. If current is in amps and resistance is in ohms, the power output will be in watts. You really don’t want to use a good conductor of electricity (low R) in this application since the equation (P=I*I*R) would then require huge amount of current to make heat. A more ideal metal (or metal alloy) is one that has a moderate resistance so you can use less current to get the heating power you want.
Most of your household electrical devices (toasters, ovens, stoves, hair driers, coffee pot, etc) use a Nickel Chromium metal alloy for heating. This alloy has a moderate resistance and retains good mechanical properties even at very high (red hot) temps. http://en.wikipedia.org/wiki/Nichrome
This application is probably using mild steel for metal. Steel and iron are not great conductors of electricity and hence they heat up a lot faster than copper.
Another option for a 12volt DC power source would be a computer power supply. They can typically supply at least 350watts on the 12volt rails. That’s enough watts to make some serious heat. The 12volt rail is used to power the main CPU (and Video cards) in PCs and CPU these days can suck down 125watts when maxed out.