Copy your plugin to the <Msg Plus folder>\Plugins folder and restart Messenger. Your plugin will be loaded by Plus and you're ready to test it. If you don't wan't to restart Messenger, make a program that executes
code:
Const HWND_BROADCAST As Long = &HFFFF&
PostMessage HWND_BROADCAST, _
RegisterWindowMessage("MessengerPlus_PluginChange"), _
0, 0
and wait 5 seconds.
I think that the info that comes with the example plugins is very easy...