Its good news that you are veering towards selenium 2.0. Please go ahead. If you want to know more about the difference:
You can try this link , from good old stack flow where it appears to have been discussed earlier.
In addition, you could try out this bit , wherein the brief history of the Selenium project is discussed. from this you could glean the path followed and the reason for the merger and thus indirectly some of the differences.
If you are thirsty for more ,there is an interesting article by Simon Stewart, which can be extremely useful to know in depth motivations behind the Selenium2 and its evolution history with Selenium1 in mind apart from the architecture and roadmap.
And finally, Google can throw up several other relevant links, apart from the ones mentioned above if you search with the keywords mentioned in the title of your question.