Unable to boot from external USB DVD drive

[elekktretterr at exemail.com.au]

Im trying to boot DragonFly live cd(latest build) from an external USB dvd
drive. But Im unable to get past the mountroot prompt. I have a PS/2
keyboard connected to it, but whats weird too is that the keyboard doesnt
work in the mountroot prompt. I tried booting without ACPI and also
without AHCI but I cannot get any further.

This box is a HP Proliant DL180 G5. It came without an internal CD/DVD
drive (which we are still waiting to get).

FreeBSD 7 installer loads fine on this box.

Any ideas?
Petr