I have solved the mp3 problem and have posted two compositions on my page.
One, a Rag, which I call the Valkill Rag in honor of the site, Valkill, which is just a short walk from my house. It's in the style of a Rag. One day it just sorta wrote itself down.
The other is an arrangement for organ of a set of variations on a hymn ("Easter Hymn") which I set for recorder quartet. For the benefit of those with no familiarity with church music, it's very much in the public domain. The tune is centuries old.
There's probably a better way of doing this, but we live and learn...