I was setting up FreeNAS 8.03 and ran into a problem when trying to boot off the USB stick as is recommended by the FreeNAS documentation.  I am using a Dell Poweredge R610, and It kept locking on the F1:FreeBSD screen. The solution to this was to go into the BIOS, into Boot Options and change the USB Emulation to Hard Disk. After this it booted properly off the USB drive.

I found the answer at the bottom of the forum the following link which has another solution as enabling the EHCI Hand Off BIOS setting. Not sure what kind of brand of server/bios this was but it may point you in the right direction.

http://forums.freenas.org/archive/index.php/t-1921.html

Hope this saves someone some time.