It sounds stranger than it really is, and can be done on a budget. In fact, most implementations of wood gas are due to budget or fuel supply issues. Production of woods gas involves a gasifier unit, where the incomplete combustion takes place, and then a filtration unit to filter out the tars and ashes from the gasifier, and delivery to an engine.
There are many types of gasifiers, depending on the fuel used and the desired effects. For fueling an engine, the gas must be very clean, to avoid tar buildup in the engine, and that's where the Imbert style downdraft works very well. Very little tar is produced with this design, so your filtering is less complicated. Also, a wide, rather than tall hopper, as in the moderator design, will allow the use of green or high moisture content fuel.
Once you have a gasifier design picked out, you will need to think about filtering the produced gas. Cyclone filters combined with a fabric or mesh filter will work well. Cooling the gas is also important, because it precipitates the tars and moisture out of the gas. So, run it through a serpentine pipe or a radiator as well.
To actually burn the gas in an engine is quite easy. Basically, you create a gas carburetor, which allows air and wood gas to mix before entering the engine. A butterfly valve on the intact will allow you to throttle the supply of fuel. Most systems require a blower to get started, to pull the gas through the system to get to the engine. The other alternative is to start the engine on gasoline and once it has warmed up, switch to wood gas. This is tricky to do, but once you get used to it, it works well.
Wood gas is not a fill up and go type of fuel. You have to start a small fire in the gasifier, and then once that gets going, shut down the air intake to the gasifier and start the engine or blower. Your engine will loose about 20-40% of its power by running on wood gas, so you have to keep that in mind. For stationary applications, like a generator or chipper, it works quite well.
Another great thing about gasification is that you can use all sorts of fuel sources from corn cobs to wood chips to paper to even plastic and tires! Anything that has oxygen, hydrogen and carbon will work, although some fuels are easier.