As a complete newbie to OpenWRt, I imaged my Netgear N600 (3700v2) and got OpenWrt running no prob.s  I  installed OpenVPN and go the StrongVpn connection working with a new interfae called VPN mapped to tun0.
What Iwant now, is to create a VLAN on a specific physical port (e.g. 1) which will route all trafic through the VPN on tun0 and get all traffic back but be isolated from the network on the rest of the box on ports 1,2,3.

The VPN of course is created through the WAN port to my external router.  So, can anyone help?

I am guessing:
Create a new VLAN:
The existing switch page looks like:

VLAN ID, Port0,Port1,Port2,Port3,Port4,CPU
untagged, untagged, untagged, untagged,off, tagged

So create  a new vlan and isolate it from VLAN 1:
VLAN ID, Port0,Port1,Port2,Port3,Port4,CPU
1, off, untagged, untagged, untagged,off, tagged
2, untagged, off, off, off,off, tagged

The somehow I need to specifc routes...

Can anyone help further?

Thanks