[Update] Apparently this was a test of sorts and the REDKit will have a full release on Monday (13 May) – look out for it then!
CD Projekt released the beta version of its REDKit set of modding tools for The Witcher 2 earlier today, but you won’t be able to get hold of it just yet because (at the time of writing,) its release made the company’s server fall over.
When it does become available again, it should be downloadable at this site. Right now it’s passworded, but that should change once it’s properly up and running again.
While you wait for that to happen, why not watch the accompanying launch trailer.