I just successfully updated my Samsung BD-P1500 Blu-Ray player using the USB port to load new firmware. I found that the unit must be powered on before plugging in the the USB flash drive so the player will recognize it. The upgrade process is automatic from that point. The process will confirm if the firmware file is compatible and is a later version and ask you if you want to continue. Click the select button on the remote to select Yes and the upgrade starts.
I used a blank 1GB USB memory stick, download the firmware file from Samsung Support direct to my laptop, then unzipped the file direct to the flash drive. nothing to it:)