To flash a sbf this is what you need to do this way is with phone off this is another way with phone on but I couldnt find it I just copied and pasted the info below :
How to Get Your Droid X Into the Bootloader
The ?Bootloader? is THE ONLY PLACE YOU CAN SUCCESSFULLY FLASH AN .SBF FILE ONTO YOUR PHONE FROM.
?Power down phone completely (battery pull, Power Button ?> Power off, etc.)
?Hold down Camera Button and Volume Down Button (lower right button and upper right button, respectively).
?Hold the power button down until the bootloader pops up (you may need to let go of the power button and then tap it again to get it to show up).
link I read it from :
Complete Droid X .sbf Flashing Guide - Droid Forum - Verizon Droid & the Motorola Droid Forum