Well, why would this be a problem? If you have HSRP on the 7200 routerr, I guess you also have a switch between the routers and the ASA firewalls (otherwise HSRPwould not be working). Well, if one of the routers fail, the pix will send the traffic over the switch to the second router (which is now HSRP active). Ideally (to be fully redundant) you should have 2 switch between the ASA and the routers

Thanks for the fast response, I understand what you're saying. We need to keep the redundancy and therefore require 2 switches between the routers and the ASA's, but does this mean we need to enable another ethernet interface on each of the 7200's?

No, This is what we do for a full failover design :

--inside--|ASAp|--outsidevlan--|SWITCH|--outsidevlan--|7200p|--WAN
                     |                                       |                                            |
              failover                        outsidevlan                        inter router link
                     |                                       |                                            |
--inside--|ASAb|--outsidevlan--|SWITCH|--outsidevlan--|7200b|--WAN
With :
ASAp : Primary ASA
ASAb : backup ASA
7200p : primary 7200
7200b : backup 7200
The ASA's have a failover cable in between them. If for example the primary 7200 looses its WAN connection, the primary ASA will send traffic to the backup 7200 via the switches.
Likewise, if the primary pix fails, the backup will take over, and send the outgoing traffic via the switching infrastructure to the primary router.
On the inside you should also have 2 switches. In cases where you only have 2 switches on the inside, and you want to setup a design as above, you can always create a non-routed VLAN on the inside switches, and use this non-routed VLAN as the 'outsidevlan'.
 

Ok this is starting to make sense, just one more thing.......in the scenario that one of those outside switches fail - obviously the ASA's will failover, but will the 7200's failover as well? They would need to or else the firewall that takes over would not be able to get to the active WAN link.

I'm assuming that the inter-router link would travese across the switches?

In case one of the switches fail (I mean really fail, like in dead :-) then both the router and the FW will indeed failover. If only an interface fails, then traffic will always have a path to the active router or FW via the outside switch interconnect.

The inter-router link is really a routed link on the routers. So therefore you need another interface on the router. It's basically a crossover cable between primary and backup router.

This is for example in case one of the switches fails. On the WAN side, both routers will still be active, which means that traffic entering the site will still use the active router (or both in case of loadbalancing). If you would not have the interconnect routed link, all traffic arriving on the router that has the failed switch connected to it, would not reach the inside, as it would not have a path to the backup firewall.

Ok, just to clarify - as I'm going to have to explain this to someone else. The inter-router link (Ethernet1), will this a separate private network? such as 192.168.0.x? Because the HSRP hello packets are sent out on Ethernet0 I believe.......

This is the IP addressing scheme we have:

HSRP Virtual address - x.x.255.1
Primary Router E0 - x.x.255.4
Backup Router E0 - x.x.255.5
Primary ASA E0 - x.x.255.2
Backup ASA E0 - x.x.255.3

Thanks in advance

Thanks for the help on this, should be able to get this sorted now.