Convert InstallShield project into NSIS or INNO project

I have an InstallShield 10.5 project that need to be converted into either NSIS or INNO installer. The project is not complicated but includes few conditional scripts, shortcuts, registry entries, dlls, fonts, etc. The project need to support XP, Vista & Win7. I will provide the InstallShield source code, and will expect the result code so I will be able to modify and maintain the project in the future.