Why would you want to do this?
Well, it will allow you to use various homebrew applications, as well as playing
games. However, the draw back to this is that you cannot play any UMD games that require anything over version 1.50.There are a number of ways to get around this, but by far the easiest and best solution is Dark_Alex's 3.10 Open Edition custom firmware.
What this does is emulate the offical 3.10 firmware (with all the new PS3 type stuff) and yet still allow you to use 1.50 homebrew apps by placing a GAME150 folder on your memory stick.
Right, before this all sounds too daunting, I've tried to make this as simple as possible, and the following is a quick guide to getting yourself downgraded from 2.80 (or lower) to 1.50, and then flashing the firmware to 3.10 OE-A to basically allow you to do whatever you like with your PSP.
The 3.10 OE-B release also gives you the ability to play any PSOne game through it's built in emulator, and this is pretty awesome as it allows people who don't have a PS3 to play PSOne games on their PSP
Here are the steps you need to undertake in order to do the above, and for those of you already on 1.50, I strongly suggest you look into updating your firmware to 3.10 OE-A
DOWNGRADING A 2.80 PSP TO 1.50
1) Download the following 2.80_-_EASY_Downgrader_0.3_by_csfreakno1_www.homebrewpsp.iphpbb.com.zip
2) Make sure you view the TA-082.jpg image included in the zip file to help determine if your PSP is a TA-082 or not. If your PSP is a TA-082 or you are unsure whether it is or not, DO NOT USE THIS DOWNGRADER, IT WILL BRICK YOUR PSP
3) Follow the readme instructions carefully, and remember to backup your Save Games and any other important files before you flash the memory stick in the instructions
UPGRADING A 1.50 PSP TO 3.10 OE-A
1) Download the following 310oe_a.rar
2) During the instructions when it asks you to get the Sony Firmware PBP files and rename them, you can get them here (already renamed) 150.PBP & 310.PBP
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Obviously I'm expecting you to read the readme's included in each of these downloads for installation instructions, but this should help you as everything is all in the /downloads area and there are no sites that currently explain this in any useful detail.
If you have any questions, please ask and I'll try to help, and please remember that I do not take any responsibility for you bricking your PSP, if you do this you are voiding your PSP warranty, but the info is here if you choose to use it.
MOD EDIT : Amended details/links to new 3.03 OE-B release 12/01/2006
MOD EDIT : Amended details/links to new 3.10 OE-A release 05/02/2007
