High Availability Design

Hello, I have:

a public/external network with one switch, a firewall network with one firewall, And an internal network, this is holding my servers and apps with one switch

We?re trying to build a High Availably solution as shown here:

so I'll be having 2 data links / switches to the public network, 2 firewalls with an Array, and internal switches to my private network

My questions are: What kind of hardware I can use as a firewall in this case? Does ISA 2006 support this diagram? Can you provide a better solution if any?

Thanks
Noor.