I can only judge by Sibelius, which is what I use on both PCs and Macs, but: though the programme itself has to be designed to run on one platform or the other, often you'll find that the files they produce are compatible and can be handled by either machine, even bounced back and forth between them - as long as each one has the ability to read the file, which any computer that has Noteworthy installed would do. So I have a feeling that the files themselves may be interchangeable.

The best thing to do is to try emailing one to a Maccie friend and find out. I'd be glad to check it for you myself but I don't have Noteworthy. There have been a number of Noteworthy threads, so if you can find an old one to resurrect, you could try asking there. (Though I'm having zilch luck with Mudsearch at the moment.)