Redundant VPN with IGBP - Newbee Question

Archived from groups: comp.dcom.vpn (More info?)

I need some help/direction on setting up redundancy in the following
situation:

Site A:
**********************************************************************
* ISP A (E1)-----PIX Firewall----3725 Router----Interior LAN *
* | *
* | *
* ISP B (Cable Modem)----------------| *
**********************************************************************

Site B:
**********************************************************************
* ISP A (T1)-----PIX Firewall----3725 Router----Interior LAN *
* | *
* | *
* ISP B (T1)------------------VPN Concentrator *
**********************************************************************

I have a tunnel setup between the two PIX firewalls which is my
preferred route
I have a tunnel setup between the 3725 (Site A) and the VPN
Concentrator (Site B).

Currently, I have to manually change the default routes on the two
3725 routers in a recovery situation of a preferred route failure.

I have tried to read up on BGP - but don't quite understand how to
configure in this situation to automatically fail over to the second
tunnel in case of a failure in the primary tunnel.

Can someone out there with BGP experience help me to configure this
fail-over.

Thanks,

Charles Jennings