I just recieved my fat psp about a month ago. Been doing some research online on if modding/hacking my psp to a custom firmware is a good idea or not. I know I'd like to purchase another psp (slim more than likely) so that way if my hacked one every craps out I'm still gaming. But my question is. Is it possible to downgrade from firmware 3.93? If so what all is involved? Thanks in advanced for all the help.

It is possible to hack any firmware.

With your already hacked PSP, you will need to create a pandora battery:
http://www.psphacksmods.com/2007/08/23/p...unbricker/

Then use this:
http://www.psphacksmods.com/2008/01/21/d...ricker-v4/

Instructions in the readme. If you need more help, post here.

What if you've never hacked the psp? I bought my psp when it first came in the gigapack a couple years ago. How do you install the new 3.90 M33 custom firmware from Sony's 3.93 firmware update?

You can buy a pandora battery from Datel. It's called the Datel TOOL battery.

You will also need to make a magic memory stick with the pandora or despertar files (search google for them, you will need them along with msipl.bin).