I have a few hundred audio files on a hard drive that I am now realizing are in the .m4a format.

I have found various "convert to" or "play using this player" type articles online but they are not really conducive to what I need.

I'm wondering if there is a basic codec package I can download and install that will let me play these in Windows Media Player 11 like I do my other .mp3 files.

Thanks!

Try using ffdshow and Matroska Splitter. Than any MP4 content (audio and
video) should play WMP11. Otherwise, you could just use iTunes for MP3, AAC, MP4 formats etc.