http://docs.sun.com/source/820-2383-14/index.html#0_27275
http://forums.sun.com/thread.jspa?threadID=5345963
To Install the OS From a USB DVD Drive
1. Connect the USB DVD drive.
2. Identify the USB device path at the OpenBoot PROM level from output from the show-disks command:
{0} ok show-disks
a) /pci@0/pci@0/pci@2/LSILogic,sas@0/disk
b) /pci@0/pci@0/pci@1/pci@0/usb@1,2/storage@1/disk <========
q) NO SELECTION
Enter Selection, q to quit: q
{0} ok
3. At the ok prompt, boot from the DVD drive to proceed with the Solaris OS install:
{0} ok boot /pci@0/pci@0/pci@1/pci@0/usb@1,2/storage@1/disk:f