i have a phat ps3 on ofw 4.xx

what do i need to get back to 3.55 i know i need an e3 flasher but what else someone said i need some usb key to down grade others said just the e3 so if you have done a ps3 downgrade b4 please tell me what you used and the best place to get it
Answer #1
Moved from Off-Topic to Helpdesk.
Answer #2
http://www.ps3hax.net/showthread.php?t=33989
this should explain it all