I can't seem to render my projects to wmv. When I go to custom settings, there is no codec under the format column. But I already have windows media encoder installed.
Custom? What file type are you choosing in the first "Render As" dialog box? You should be scrolling down to Windows Media Video there before clicking the Custom button.
Are you running Windows XP with SP1 by any chance? Or have you installed Windows Media Player 9? If so, try installing the following and see if it fixes it: