With 3e and the OGL, it was fairly easy (you had to have at least 10 percent OGL content, and slap the D20 system logo on it somewhere, attach a text copy of the OGL, and fill out a little form and mail it to WoTC under this situation you even could post monster statblocks), however with 4e and the new license WotC has its a bit of a mess. One has to fill out a different form now, there's more restrictions, and I think you even have to wait for some sort of approval... but the 4e liscense rules are second-hand knowledge to me...