Daniel, don't expect anything new with the PC version! It is the most bare bones port they could have possibly done. It doesn't even come with the nice CG movies from the PS3 version, instead it's the compressed Xbox 360 versions (the entire port is a direct rip of the Xbox version).

I want to get it on STEAM. Does anyone know how to buy game from STEAM? It's my first time, so I have no idea.
In terms of buying from Steam, it's pretty easy. Head on over to http://store.steampowered.com, 'Install Steam' if you haven't done so already and create an account once it has installed. Then you just find the game you want to buy on the client, hit 'add to cart', and Steam will take you through the buying process and ask you where you want to install your game. Then hey presto, it'll download and install it for you. All you have to do once it's finished is hit 'Play'.