Raphaël 

I see I'm talking to a pro :-)

Can you be more specific on your hardware?
Motherboard, Processor, which nic's how many, cf slot and case?
Do you also have any performance benchmarks?

I will be using m0n0wall for routing 2 different subnet's of public ip
adresses with firewall function.
For peak performance I will be needing 100 Mbs.

Oops another question came up:

What should I use for routing and firewalling 2 different public
subnet's behind the router?
From the documentation I understand to disable NAT and you have only a router?
Do I need to assign then 2 public ip's one for the WAN port and one
for the LAN port?
What is the Proxy ARP function in this setup?

http://m0n0.ch/wall/docbook/faq-no-nat.html
http://m0n0.ch/wall/docbook/faq-ipalias.html

I'm sorry for all these question's ;-)

Maarten