Jakg is right.
You can't upgrade the 8200 in the sense that you are removing the GPU and replacing a new one into the PCIe slot. You can, however, insert a dedicated GPU into the PCIe 16 / 8x slot. If you look
http://www.nvidia.co.uk/object/geforce_8200mgpu_uk.html, there are indeed PCIe slots. Anything that has dedicated ram to the processor will probably be better than that in your board. $50 can get you a 9600GSO which is probably 10x better than that. (not sure about in UK, etc).
Turbocharge the performance of your GeForce GPU. Plug it into a GeForce 8200 motherboard to enjoy GeForce Boost and enhanced graphics performance.
I believe that is talking about another card in works of Hybrid SLI. In advertising the 8200 motherboard of its graphic capabilities, it is selling the fact that a dedicated card is not needed, and really just a marketing plot. These IGPs can't run Crysis without looking like Doom 1, or Virtual Tennis without looking like Pong, or Virtua Fighter 5 without looking like VF1 running on the Saturn =D. It is anyhow better than a P35 without a graphics processor embedded in the motherboard (especially if you can't soup up one to start doing some homework) or Intel GMAs.