http://comserver.googlecode.com/svn/.../comDemo/coder
Extract the the codec source from
http://www.webmproject.org/tools/vp8-sdk/ to the 'includes' directory.
Configure the project settings to the correct includes.
On your flipping.... So then, you'll have to flip/unflip the image output, which is unflipped I think, and set/unset the coder_dll flip flag. Winamp is not flipped at this time, so flip the output and toggle the flip flag. Winamp will still be right side up then.
Also check versions. 'Flip' shouldn't change between versions, but output can look funny. This was 9.5 from january.