What's the difference between natural gas, coal, and biomass?

The argument for biomass in place of fossil fuels centers in terms of GHG emissions has to do with the net balance of CO2. As Mr. Del Padre alludes to, the Carbon Cycle for biomass is considerably shorter in time than fossil fuels. While fossil fuels are a form of carbon sequestration, the time scale is on millions of years. The time to harvest energy crops is on the order of months to years, such that the CO2 removed from the atmosphere by plants while growing is equal to the CO2 upon combustion (or other processing.) However, biomass is also less energy dense, requiring more biomass than say coal to produce the same amount of steam to drive a turbine. E85 ethanol is roughly 30% less efficient than gasoline to drive a FlexFuel car, so there are trade-offs. Of course, the method of utilization (combustion, co-firing, pyrolysis, liquefaction) has a large impact on the net GHG emissions, and so it's difficult to suggest a blanket difference across both process and biomass type. There is a large literature on Life Cycle Analyses for a variety of biomass sources and energy production scenarios, which is a good place to start.