Is it possible to bridge 2 routers together so that both LAN's are on the same subnet and then encrypt the traffic between the two routers across the WAn segment transparently via IPSEC?

I have a 7960 running the SIP FW, and I have 2 7914's to attach to it. Are the rumour's correct that they don't work when using SIP. If they do can someone tell me how to get them to work properly. Do they require different software loaded to work in...