There is desktop linux support for PPtP (the MS variant) with tools, these could probably be ported to the N800. The kernel has the PPtP support too, but this is possibly not enabled in the N800 version so you would have to build your own.

There is however OpenVPN available already, and where I work we switched from PPtP to OpenVPN and thus that's where my interest is so unfortunately I'm not raising to the challenge of getting PPtP to work -- I'm more interested in getting the OpenVPN support integrated into the network applet, as now it's a hassle to use.