For firewalling I have an IP-Less bridge running OBSD3.0 and a Firewall behind that running OBSD3.1 Funny both boxes are old HP Vectra VL's with 90mhz pentium processors a whopping 16 megs of ram and 500 meg HDD's. I don't believe I've ever dropped a packet. And running a top on my systems show a couple of computers 100 idle all the time. Interesting.
For firewalling OpenBSD is the ONLY way to fly!