I know Windows XP has gotten a bad rap, especially among those who loved Windows 2000, but the truth is that XP included a pretty extensive game compatibility mode for older Windows games, which, at least in my experience, worked quite well. If you stick to the 32-bit version of Windows XP (and don't connect it to the Internet, for obvious security reasons), you'll have quite a range of downward compatibility, with Win9x games, Win3.x games, and even quite a few DOS games. I believe Windows XP emulates Sound Blaster out of the box in DOS instances, but VDMSound improves on that considerably, adding support for more Sound Blaster variants and MPU-401 MIDI emulation/passthrough/mapping.
So maybe you could try running Windows Embedded POSReady 2009 (a special edition of Windows XP for point-of-sale terminals and such, which continued to receive security updates long after the regular Windows XP ceased to be supported, although you probably stil shouldn't connect it to the Internet if you don't have to), and then installing VDMSound on top of that? 🙂
EDIT: I just read the title of your thread again, and you're trying to get this to work with a USB MIDI adapter. As far as I know, that definitely requires something like VDMSound, and therefore wouldn't work in Win9x.
I believe your options are limited to the following:
- If the system supports it, use an ISA or legacy PCI (not PCI Express) sound card that supports MPU-401 compatible MIDI at legacy I/O addresss 0x330, through the game port (requires an adapter cable, which is commonly available)
- Install VDMSound on a Windows version from the NT family (NT4, 2000, XP, POSReady 2009)
- Buy an MPU-232, which is an RS-232 to MIDI interface, compatible with SoftMPU. You can also patch a number of DOS games to add native support for it.
- Use a build/fork of DOSBox that allows you to pass through MIDI from the emulated DOS game to the MIDI device on the host OS.