As an emulator of MacOS, I know that there was PearPC, however, I think that one of the creators passed away and most of the project was shut down. You can still get a download of it, but I would tell you that the emulation is rather slow, so if you attempt to use it, be ready to wait. You can download the emulator here:
http://pearpc.sourceforge.net/
The task of course, would be to find the ROM for MacOS 10.3, but if your really looking for it, it's out there. Unfortunately, this post is more informative than a surefire method to emulate, use at your own risk.