Shortly after I boot FreeNAS 8 64-bit (its installed on a 2Gb drive which is normally enough for a BSD), the kernel kills python with "out of swap space" and the WebGUI returns error 503 / Service Not Available.
You say you are using a 2GB key.....if you can, try with a 4GB key. FreeNAS is 2000MB and every 2GB key I own is actually ~1.9GB in size just a tiny bit to small which makes FreeNAS operate in unexpected ways. Try it with a 4GB key.