Maybe your problem is that there is a plethora of VPN clients for
both OS X and Windows, some of them using non-public protocols.
Please specify a bit better what you do want, so we can tell if
it is doable. VPN (even with the Layer 2 specified) is a far too
wide specification.
For open source connectivity, my favourite is OpenVPN, although it
runs on top of UDP, instead of the Layer 2 mess.
--
Tauno Voipio