Ladies and Gentlemen, start your Creation Engines! Today, Bethesda has finally released its main modding tool for Skyrim, The Creation Kit. To download, start Steam and go to View/Tools and download Creation Kit.
There's also been a free High-Res Texture Pack DLC released, so be sure to grab that from Steam as well. For more on the Creation Kit and how to use it, go to Bethesda's official Creation Kit Wiki.