Raduga uses the DirectShow filters (codecs) that are installed on your Windows system. As soon as there is an MP4 codec available, you will be able to use it with Raduga.
I recommend you to try the patent-free Ogg-Vorbis format. It is more widely used than MP4 and there is a free DirectShow filter available from:
I installed both those DirectShow filters, but when I try to play an MP4 AAC audiofile (created with Nero 6) in Raduga, the Windows program error message appears: "Raduga has generated an error and will be closed by Windows."
So I'm sorry to report, that I didn't get it to work.
A question mark (?) in front of the title of the MP4 AAC audiofile in the Raduga playlist indicated that Raduga still didn't recognize the MP4 AAC audiofile format.