How is carbon distributed among the atmosphere, the oceans, the biomass and the unburnt fossil fuels?
1.How much carbon is there on Earth?


Taken as whole, the Earth is estimated to be 730 parts per million carbon by mass. 

So $4.4 \times 10^{21} kg$ 

http://quake.mit.edu/hilstgroup/CoreMantle/EarthCompo.pdf


  
  How much carbon is there in the atmosphere (in the form of CO2 and CO)?
  


$3.1 \times 10^{15} kg$ CO2 and insignificant CO, so $8 \times 10^{14}$ kg of C. 


  
  How much carbon is there in the oceans in the form of CO2 and CO?
  


Carbon of all forms in the the ocean is $4 \times 10^{16} kg$

http://ioc-goos-oopc.org/documents/oosdp/oosdp_br5.pdf


  
  How much carbon is there currently in the biomass?
  


$8 \times 10^{14}$ kg (not including soil)

$2 \times 10^{15}$ kg (if soil is included)


  
  How much carbon is there left in the form of fossil fuels?
  


$5 \times 10^{15} kg$

http://www.gcrio.org/CONSEQUENCES/vol4no1/carbcycle.html

(This could be an underestimate, depending upon what you consider to be "fossil fuel"; methane clathrates are estimated to hold $10^{16}$ kg of carbon)


  If possible, i would also like to know how this distribution has changed, for example, over the last 100 years (in particular, how much carbon from the fossil fuels has been burnt over the last 100 years).


The amount of carbon in the atmosphere has increased about 30% since pre-industrial times, and the amount in biomass, not including soil, has decreased about 10%.  Amount in the oceans has not changed significantly.