Metasynth Pro 4 (the 24 bit version) is not compatible with Leopard. UI software, the developer, said that they are working on it (and have been for the past year and a half). I installed the Leopard compatible-16 bit version, called Metasynth 4, on workstation ST9.6, 9.7, 9.8, ST4, ST5 and ST8
NOTE: When you launch Metasynth, the top menu bar and the dock disappear. To see either the top menu or dock, just mouse over their normal area and wait a few seconds. They will re-appear.
Additionally, Metasynth pauses on an opening info screen for about five seconds before showing you the main work window. If you’re the impatient type, just click on the green check mark.
If you don’t know about Metasynth, check out UI Software’s website.