It would be nice to connect to the x server via a (secure, vpn?) remote desktop (vnc?) protocol. I could then browse the internet from the location of the host, or the intranet / home PCs.
It won't probably work for XBMC video playing
If you just want to browse the internet from the host and are using a VPN you are already done.
Use OpenVPN and redirect the gateway; you can then browse the internet from the location of the host.