GRE tunnels

I don't believe that either supports GRE.

A. No. The Cisco Catalyst 3750 Series can switch "transient" GRE tunneled traffic in hardware at wire-rate but it cannot act as GRE tunnel end-points.

On the other hand, there is this, which implies that there is GRE support:

If a generic routing encapsulation (GRE) tunnel is created between the Catalyst 3750 Switch and router, and if the switch forwards the unicast packets, then there is an increase in CPU utilization.

The high CPU utilization is due to the hardware limitation of a Catalyst 3750 Switch. The switch does not support tunnel interfaces for unicast routed traffic. Only Distance Vector Multicast Routing Protocol (DVMRP) tunnel interfaces are supported for multicast routing in the Catalyst 3750. The Catalyst 3750 Switch can be configured with the tunnel interface. However, because of a hardware limitation, it cannot switch those packets in hardware. This causes all the packets routed through this tunnel to be switched via software. The larger number of packets forwarded through this tunnel increases CPU utilization.

There is no workaround for this problem. This is a hardware limitation in the Catalyst 3750 Series Switches.

yes I have seen the last document which has a gre tunnel running between a 3750 and a router, i know there is layer2 tunnel support but that wont do me, there are routers in the network however they arent owned by the client (owned by the teleco) and therefore we don't have access to configure them.

Any other way I can get multicast traffic from one network to another over a wan between switches?

Flamer.

We are routing through a private network called remote office, it actually doesnt permit multicast traffic across it so the multicast packets have to be encapsulated/tunneled first.

Flamer.

You need the advipservices feature set. I use tunnels on 3750's and

GRE doesn't support multicast on the 3750 even when you are running advipservices.