For those already familiar with the flavors of Linux and FreeBSD, is quite simple:
sudo dd if=openmediavault_xxxx.iso of=/dev/sdx bs=4096
Of course, substitute the xxxx's with the actual name of the iso and sdx for your USB drive's name designation. For those of you that have never touched *nix and/or are stuck with Windows, try this pretty dd replacement:
http://unetbootin.sourceforge.net/
Run the application (as admin), and simply select the Diskimage and ISO option, and point to the image file for OMV. Select 'USB Drive' for type, and the drive letter for it, then OK. Couldn't be any easier guys.
And that's it! Now go ahead and boot the new drive with your future OMV server.
*Note: This is assuming that you are installing to a regular hard drive or SSD device, not for installation to a USB flash drive. There are other guides for that.