User blog comment:Topher208/Update on New Skin & Upcoming changes/@comment-1852035-20101020120839/@comment-961279-20101021032055

Make a .png picture that's 250x65 and select what color is to be used for transparency when you save it. Then go to the "My Tools" at the bottom of any screen and click on "Theme Designer". You will then be able to upload it as the wordmark.