VPN failover

[woongko]

Hi,
My project is to set up site-to-site VPN failover between two offices. I need help with how to configure and IOS image to choose for a router. Here is the simple design.

Cisco2801 --------<ISP 1>---------- Cisco 1721
| |
-----------<ISP 2>-------------

2801-site has ERP and Terminal servers so that 1721-site employees logon remotely for everyday work. If ISP 1 goes down, 1721 should take ISP 2 AUTOMATICALLY to connect to ERP application.

[Specs]
2801: HWIC-4ESW, 128/64MB, c2801-ipbase-mz.124-1c.bin
1721: WIC-4ESW, VPN module, 96/32MB, c1700-k9o3sy7-mz.12.3-8.T11.bin

I have two questions:
1. I can think of a one-channel site-to-site VPN. But I am not sure how VPN failover will work with two channels between two routers. We're not using BGP. I found this doc but not clear about how OSPF works for failover between two routers.

http://www.cisco.com/en/US/tech/tk583/tk372/technologies_configuration_example09186a00800a43f6.shtml

2. Which image should work for 2801 router? Does any image above 12.3(T) with "Advanced IP Services" work? Would c2801-advipservicesk9-mz.12.4-1c.bin work for this project?

I'd appreciate any help.
Thanks,
Dave