[GUIDE] How To Boot Multiple Firmwares On Your PSP
The first thing you need to know is that your going to be backing up and restoring your nand; while backing it up is relatively harmless, restoring should only be done if you have at least 75% of your battery or your on AC. I am not responsible for any damage done to your PSP, only do this on hackable motherboards.
Now that we have that out of the way its time to get everything you need:
1) A Hackable Motherboard
2) Rain's UltraLite MMS Maker for 3.90 (download)
3) The 3.90 Updater Eboot (download)
4) nandTool v.4 NEO by cory1492 (download)
5) A Pandoras Battery
6) A Fully Charged Battery or AC
Ok its time for another warning, as long as you don't turn off your psp, pull out the battery, or remove the AC cord nothing should go wrong :)
First thing you need to do download all the files listed above, and get a pandoras battery. Once you have that done now its time to turn your memory stick into a MagicMemoryStick :) Ok now unzip the Rain's MMS Maker and copy the 3.90 update eboot to that folder. Rename the eboot from "eboot.pbp" to "390.pbp". Using Rain's MMS Maker select the Make MMS button. When that's finished you can close the window. Now open and unzip the nandTool zip; you should get two folders elf and psp, all we need is the elf folder. Copy the elf folder to the root of your memory stick. Now go into the elf folder and cut(Ctrl X) the file "nandTool_040NEO.elf" and go back to the root of your memory stick; go in to the "TM" folder then in the "DC5" folder, the finally in the "kd" folder and paste it there. Now still in the "kd" folder cut the file "resurrection.elf" and paste it into the "elf" folder in root of your memory stick. Now go back to the "kd" folder, and rename the file "nandTool_040NEO.elf" to "resurrection.elf".
Now boot your psp with your pandora's battery holding the "L" trigger. After the splash screen you should be greeted by a WARNING screen, read through it. Once you get through that you will be presented with a main menu, choose "Dump from NAND". You should get a screen like this, with a different file name depending on your psp:
Once that is dumped exit and remove your pandora, now connect your psp to a computer and go into the "nandTool_dumps" folder, and rename the file to the firmware name (ie 5.50 GEN-D3, 6.20 OFW) or whatever you want (remeber to put the .bin). Now you'll want to back that sucker up on your computer ;). Now install any new firmware on your PSP, lets say OFW, install it like any other firmware then use your pandora to get to the nandTool menu. Again dump it, then rename it to what ever you want on your pc (back it up too).
Now that you OFW on your PSP you've probably decided that you want to go back to CFW. No fear we can do that with nandTool :). Get out your pandora and hold "L" trigger to start it up. Now this time instead of backing up (we already did that) its time we write to nand. Remember that this could be dangerous so be wary. Go down to the "Write to NAND RAW" option and press cross. It should list your back-ups kinda like this:
Choose the FW you want on your PSP and press cross, you should be greeted by another option screen, choose "Write full image". Now you will be presented with a final screen that asks you if you wish to proceed, read it. After you finish shutdown and remove your pandora, welcome back to the world of CFW :) That finished my tutorial, hope that helps, if you have any questions feel free to ask them.
Notes/Last Minute Facts:
DCv5 is needed because that is the last version of DC that allows the use of .elf files (what nandTool is)
If you get a bad block message, its fine. PSPs with bad blocks are routinely sent out by Sony because your firmware can route past them 
You can keep both your pandora menu (DCv8) and nandTool (DCv5), all you have to do is edit the config.txt in the TM folder
Backing-up and restoring your nand can be safe and easy as long as your careful