I don't think TW1 is a requirement. There isn't all that much that comes into play from the first game into the second. TW1 does give you a better understanding of the world, but other than that, I don't think you really need it to understand TW2. That doesn't mean I don't recommend playing TW1 because it is a great game.
I think for TW2, you just need to play through the game a few times to understand what's happening. Reading some posts here may shed some light on things that you didn't fully grasp before, but otherwise, just going through everything a few times will make things clear.
