Had some problems booting the latest pfSense ALPHA on my ALIX.
Solution (maybe, because I already booted NanoBSD succesfully in the past…):

http://doc.pfsense.org/index.php/NanoBSD_on_WRAP
http://doc.pfsense.org/index.php/ALIX_BIOS_Update_Procedure

The pfSense > 1.2.3 on ALIX by PieterB's blog, unless otherwise expressly stated, is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 Belgium License.