There is now a RISC OS Squeak 4.0 with actual sound output available for testing - try http://www.rowledge.org/tim/squeak/Squeak3-9c-RISCOS.zip
to download a bundle of the entire squeak setup, including the DeepKeys and SharedSoundBuffer modules, the Squeak .source file already installed and the image/changes file ready to go.

And if that seems to work, you might try a very sketchy Scratch try-out by downloading http://www.rowledge.org/tim/squeak/Scratch-RISCOS.zip 
– but you’ll need to have grabbed theSqueak package first in order to have the deepkeys/ssb modules.

tim
--
tim Rowledge; tim at rowledge.org; http://www.rowledge.org/tim
There are two ways to write error-free programs; only the third one works.