My first recommendation is to use another method of install, see: http://undeadly.org/cgi?action=article&sid=20100404103735
If you really want to continue: Is the BIOS up to date? Also, is there a setting for USB mode in the BIOS? Sometimes listed as USB Drive emulation, or similar. I know that most of this seems basic, but even the best of us need reminding now and then.
