Hi,
How's the connection from the two hsrp routers to PIX? (y idea is based on your input here..
Since the routers are running HSRP, both of the fastethernet interfaces facing the PIX should be connected to a hub or switch (in same Vlan).
Connect your PIX inside interface to the same hub/switch (same Vlan).
The route inside in PIX should point to HSRP virtual IP, not physical IP on each router interfaces. This allows PIX to 'see' only 1 IP to represent the two routers, as the routers logically exists only as single router to PIX. On the router, set the default route (or specific route) to PIX inside interface.
Internet -> router <--> outside: PIX : inside -> hub/switch <- HSRP virtual IP : routers ->
Is there any other info that might help us on your current setup?
Rgds,
AK