To play sounds other than "harpsichord" or "Boing," you must make the data for the sound available. The actual data for sounds are stored in resources. HyperCard looks for the resources in the current stack, the Home stack, the HyperCard application, and the System file. If the sound exists in any of those places, it will play.
You can use the ResEdit application to move sounds
(resource type snd) among stacks. If you are going to give your stack to other people, put the sounds it uses into the stack itself rather than Home.