I just installed pfSense on an old PIII server (intel L440GX mainboard), and for whatever reason, it would freeze when booting. By disabling ACPI, it boots OK, so I did some searching for information on how to disable ACPI for every boot. I found that this is possible by adding:
to the end of /boot/device.hints from the diagnostics -> edit file menu option.
I'm now using the most recent build of pfSense (1.2-RC3) on several machines and I'm very pleased with the results.
The cool thing about this mini-project was that I was able to replace a VPN gateway router which was running on debian without too much trouble. I was a little nervous about doing that, especially remotely, but it worked out well. I first created a third VLAN on my Cisco router for a new subnet, just in case I wasn't able to do the switch. Then I moved the current gateway address, keeping the public WAN address active. Then I switched in the lan ip of the new pfsense vpn firewall router, setup IPSec and tested it to make sure it was OK. Then I made the LAN nic of the old VPN server a dhcp client, tested it, then did the same for its wan port, and added the port on the cisco switch to the second VLAN.
Thankfully, it all worked! :-)