AT90USBKEY Flashing Guide
I tried doing this in Windows 7 x64 and failed both on my Mac and my laptop. Some people say they got it working but i did not. I had to use a 32 bit copy of Windows XP to make it all work.
MAKE SURE YOU ARE ON FIRMWARE 3.41
1: Download and install Flip from Atmel's website. Download the one with the JDK if you don't have Java installed on your system (or don't know if it has been installed)
2: Attach the device to your PC, it will detect as a regular USB stick and you should be able to see a bunch of files on it
3: Press the RST button, then press HWD button (while still holding down RST)
4: Release RST (make sure to still hold down HWD)
5: Release HWD
6: At this point, Windows should detect an unknown device and ask for a driver. Point it to your flip installation directory \usb folder eg: c:\program files\flip\usb
7: It should then show that it has loaded the device AT90USBKEY DFU Mode and you should NOT be able to see any files on it
8: Launch Flip, click the select device button, and pick AT90USB1287
9: Click the USB Icon then select USB and click ok. You should see more icons available now
10: File -> Open , Load your HEX File (WHICH HAS TO BE THE AT90USBKEY ONE)
11: Click the Erase rom icon, hover over them it will say what they do
12: Click the Program Button
13: Click the Verify Button
14: Click the run program button and the LED should go RED (for me, XP started detecting a 6 port USB hub at this point)
You're done, unplug it.
If you have a fat unit, click the power switch off on the back, connect the USB cable from the AT90 to the 1st USB port, click the switch on, make sure there is no disc is the drive. Turn it on, press eject right away, you should hear 2 quick beeps
Slim do the same except unplug the power cord as there is no switch
You will need to unplug or use the back switch each time you wish to boot your PS3 with the Jailbreak
You should see install packages now under Game menu
UPDATE: I have been permitted to attach the patched .hex file for the AT90USBKEY but not the Backup Manager.