I've made some progress on this topic -
Get the archive .
Put OpemMPT_VSTi.dll to your VST plugins dir, put OpenMPT_VSTi.exe to mptrack dir.
Run VSTi host (even OpenMPT itself will go

) and load .dll - it will show config dialog for the first time (you'll be amased how do I like to write config dialogs

). After you finished with config (typically change path to .exe from archive), restart VST host. Then, when you load .dll, the mptrack window pops up (note "VSTi" in the title). Load some song in mptrack and then send MIDI keys to VSTi DLL:
C-4 to A-4 to start playing patterns 1-10 (in theory, right now it just starts playback from current pattern).
C-5 to A-5 to mute channel 1-10 (mptrack GUI won't show it, but it is muted, really

).
B-5 to stop playback.
Hold A#4 when hitting some key to toggle On Transition mode - that's it, mute toggled and selected pattern played at the end of current pattern (that's the only way to go to some pattern for now).
Hold B-4 and type large number with several keypresses - the selected channel muted / pattern played when you release B-4 (doesn't work yet).
Yeah. Bugs are not just possible - they are expected

, so please report them

.
Oh. That's taken the whole week to code, and it's still prerelease.