[cmpahar]

I highly recommend Codebender.cc which is an Online IDE for Arduino. It has code completion, a lot of already included libraries (you can request for your own), a huge list with examples, the ability to share your code or find another user's code and its on the cloud.

For setting up your computer, you don't need to install any special heavy development kit except Codebender's plugin. I remember that after completing a getting started guide in 5 minutes I was able to program my Arduino board!

Cheers