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What's the difference between Pokemon Diamond, Pearl and Platium?
are they all the same like when the orginal pokemon blue, red, and yellow came out on game boy color? blue and red is like diamond and pearl. Platinum is the newer one like yellow?... I havent played since fire red and the green version for nintendo advance.... so im kinda behind 
but i plan on buying a dsi xl for christmas and i wanna catch up!
Yes, they are the 4th generation version of Red, Blue and Yellow. Every generation has the 2 main games, which have differences in which Pokemon appear as well as (in some) which legendaries you battle and slight story line differences, such as Teams Magma and Aqua in generation 3.
Red & Blue; Yellow
Gold & Silver; Crystal
Ruby & Sapphire; Emerald
Diamond & Pearl; Platinum
And now, Black & White, with the extension not yet revealed.
The main difference you'll find is the section that focuses on Palkia and/or Dialga. In separate games, one or the other will appear to you, and in Platinum they both will. Platinum also has a whole bunch of other Pokemon (I think it's close to 60 of them) added to the Regional Pokedex, and more legendaries you can battle, as well as the Distortion World becoming available. There are many gameplay changes and storyline changes, but it is essentially the same as the other 2, only adjusted, as usual.
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