It is not helpful to spread the myths bandied about by computer shop/rock instrument shop 'experts'. These people are as likely to be computer wizards as your local newsagent. Some know what they are talking about others don't.

"Microsoft is dropping all MIDI functions in 2010"

They are not! There were problems running WMP on a few sub releases of Windows7 (Vistas future replacement). If you read the later posts on the link below, you will see they have been resolved.

Sevenforum

As Windows7 will be around for the next few years midi functions won't be disappearing for a while. In any case MS have no control over software companies creating packages exploiting midi input files or devices to send to sound system.

"A clerk at the local rock instrument store told me that Windows Vista support of MIDI is 'crappy'"

I run midi files on XP Pro and Vista Home Premium. Support for midi on Vista is no better or worse than on XP. The output quality depends on the sound card and its drivers not on the Operating System. (XP Home is pretty much XP Pro with some functionality taken away. Vista is .... er well lets say roll on the full release of Windows 7).

In your opening post you said that you cannot open any midi or NWC files. In which case the problem is unlikely to be with Noteworthy. It is possible that the file 'Sndvol32.exe' in

Windows\system32\

has been corrupted or is having compatability issues with your sound card drivers. Try running Windows updates (do full updates not just express) and look for updated sound card drivers. If that doesn't resolve the problem replace the file Sndvol32.exe. Sndvol32.exe can be extracted from a Windows XP disk.

Sndvol