VMPK on Windows will play using the Windows Synth and the gm.dls soundbank (a Roland soundbank).
You CAN make .dls files using a program called Audio Compositor 4.0.
The issue here is that once your new dls file is made, you have to rename it to gm.dls, then replace the
gm.dls in the SysWow64\Drivers folder (for 64-bit Vista).
After reading a bunch on how DirectMusic reads DLS, I noticed that you can programatically change
Windows Synth (dmsynth I think) to another dls, but there is not an "interface" to it in the OS (as far
as I've found anyway).
So (theoritically), with a few modules of code, you could probably have a way to point Windows
Synth to another dls file.
That would be cool.