Installshield project converters are disabled.How to enable them?
From IS Help (my underlining):
"InstallScript MSI projects created using InstallShield, InstallShield DevStudio, or InstallShield Developer can be easily converted to the InstallScript project type"
The inference - and my experience - is that if the MSI wasn't created by IS, you can't covert it. Why would you want to, anyway? What do you need to do to the MSI that converting it to an ISM would be necessary?
Just do an admin install (msiexec /a...) and voilá! You have the source files.
Either add them in to the MSI or, if you want to turn it into a project, start a new project, start capturing, "re-install" the app using the source files you just extracted, then add any registry junk you need.