Not sure exactly how/where to place this, but it ought to be added in some form.
Here's where I found it and all that is need is to open the loader prompt during the CD/DVD/USB boot (by pressing 2 or ESC) and adding the following line:
set debug.acpi.disabled ="hostres"
and then booting with
Once the USB key has booted you can add the line
to /boot/loader.conf, if you intend to use the key again. In any event, once you have installed FreeBSD 9.0-RELEASE, you still need to add this line to /boot/loader.conf.