With a few post-install corrections, pfSense 1.2.1 works on ALIX with a hard disk drive. Use a regular PC with a 40–>44 pin adapter to install pfSense selecting the "embedded kernel". After the install is complete reboot and the restart off the CD a second time. This time select option 8 to access a shell instead of install.
cd /tmp
atacontrol list
find your hard disk drive in the output above
you will need it in the commands below
should be something like ad0, ad2, ad4
replace the "X" below with your drive number
mount /dev/adX /mnt
cp /mnt/boot/mbr .
echo 'hw.ata.ata_dma_limit="4" ' >> /mnt/boot.loader
vi /mnt/etc/fstab
change the drive shown to /dev/ad0 instead of /dev/adX
umount /mnt
fdisk -B -b mbr adX
(remember to replace the "X" with your drive number)