Are their binaries of GDAL available already compiled with PostGIS Raster suppport?
Yes. Check out the page GDAL Binaries page. Any compiled wiht PostgreSQL support should have PostGIS Raster in them. We know for sure the following windows binaries have PostGIS Raster built in. FWTools latest stable version for Windows is compiled with Raster support. PostGIS Raster is undergoing many changes. If you want to get the latest nightly build for Windows — then check out the Tamas Szekeres nightly builds built with Visual Studio which contain GDAL trunk, Python Bindings and MapServer executables and PostGIS Raster driver built-in. Just click the SDK bat and run your commands from there. http://vbkto.dyndns.org/sdk/. Also available are VS project files.