James,
One other thing worth checking is the network card in the Untangle box. Did you buy an appliance, or build your own Untangle box? If you built your own, be aware that not every NIC supports VLAN tagging. Many desktop NICs will strip away VLAN tags before they reach the OS. If you bought an Untangle appliance, then you are fine. If you built your own box, double check the specs for your network card to ensure that 802.1q trunking and VLAN tags are supported.
Don Pezet
Host, ITProTV

I asked around the office and none of us have any experience with OpenWrt. I'll see if I can dig up a compatible router and figure out how it handles VLANs, but I can't make any promises on this one.
Don Pezet
Host, ITProTV