i'm using vista64, i installed Paint.NET with the appropriate 3.5 .net package, i installed the VC x64 redistribution first and couldn't see your plugin, i installed the VC x69 redist and still can't see your plugin... (it's in ..\paint.net\filetypes\)
damn.
ps: i can see the default .dds plugin working fine.
ps2: i added the icon format plugin (icocur.dll) and can see them fine (.ico, .cur, .ani)