That feature is usually a hardware thing... well the good background removing things at least...
If it were to be software, you'd need a blue screen or something of the sort...
none the less, those software would need to really powerful, so i dont think a little MsgPlus plugin could be powerful enough to work with your webcam hardware to remove a background. Your webcam on MSN Messenger is pretty much processed through the webcam drivers, so unless you manage to soup up the driver or have a webcam that can directly do that from the hardware, it isnt really possible.
