Update #1: Dark_AleX, Yoshihiro and Mathieulh have now released the 1.50 to 1.00 downdater. Remember that to install this program, you will need the help of someone with a 1.00 PSP, and as always there is a risk to brick your PSP whenever you write to the flash memory. Be sure to have your battery charged and your PSP plugged into the power source to make sure you do not lose power while doing this. The steps are as follows, for the person with a 1.00 PSP, and the 1.50 PSP:

Instructions for the 1.00 user:

- Copy the downhelper100 folder to /PSP/GAME/ and start the program.
- It will dump your flash and your ipl to the memory stick. After finished, the program will exit.
Send the folder created at the root of your memory stick called "DOWNDATER" to someone with 1.50 to allow him to downgrade.

Instructions for the 1.50 user:

- Copy __SCE__downdater100 and %__SCE__downdater100 to /PSP/GAME/
- Get the DOWNDATER folder from your friend with a 1.00 version PSP and put it on the memory stick.
- Get the official Sony 1.50 update and put it under /PSP/GAME/UPDATE
- Start the program.
Note: You need to set the language of your psp to either english or japanese before starting (anyways, it will advise you if you don't have that requirement and it will exit safely). Also, connect the PSP to the AC adaptor.
- After a confirmation with the X button, you PSP will start to flas to 1.00.

DO NOT REMOVE the memstick and DO NOT shut down the PSP.

After it is finished, the program will tell you to restart the PSP manually, and you will have a 1.00 PSP. Remember, this will flash your PSP's flash memory and you could potentially brick (break) your PSP.

Before downgrading, make sure you meet the following requirements -
Your PSP is not a TA-082. This downgrader has you to be tested on a PSP with this type of motherboard. (If you do have this PSP version, it may result in a brick). [Find out if you have one!]

If you are willing to try this and know the possible consequences, you must enter a password for the file.

The password for the download (when you extract) is: I_Use_It_At_My_Own_Risk