I am running (more or less) FreeNAS 0.686.2 and 0.69 in VBox 1.5.4 OSE and 1.5.6.
(FreeNAS is a NAS-firmware based on FreeBSD: Http://freenas.org)
During boot the process stops at some point with the message:
'Fatal trap 12 page fault in kernel mode'.
I have to switch off the VM one or several times untill the system boots correctly. Beheaviour is quite similar to what I observed under OS/2. FreeNAS is more verose during boot, so I could catch that message, while OS/2 just silently hangs. See also here:
http://forums.virtualbox.org/viewtopic.php?t=5003
Ingo