在A9看见的（最近一直在玩儿VP，没事儿查攻略的时候看到的= =~）
下面是原文

复制代码 Yes, you have read the title right - 2.50/2.60 Downgrader. Dark_Alex, along with Mathieulh and Yoshihiro from SonyXTeam, have released the first working 2.50/2.60 downgrader. We have seen several betas over the past few days, several of which have been confirmed as non-working. However, just a few moments ago, Mathieulh released a beta version of the upcoming v5 of the downgrader. Dark_Alex is current asleep as I am typing this, and thus can not release the final version (non-beta). If you choose to use this downgrader, use it at your own risk! The IRC (Internet Relay Chat) is full of discussion over this downgrader and we are right there, getting every bit of information for you. Now, you are probably wondering how the downgrader works after the previous attempts failed. Mathieulh says it best in the release thread - "It uses some sony libraries found in the 1.50 updater to perform the most critical steps, the logical format of the flash, and the ipl writing. See technical details for more info about how it works." The technical details can be found in the release thread. Now, you are all wondering - "Well, how the "hell" do I use this?" Here's your answer- The downgrade process is separated between two people, a 1.50 user and you (2.50/2.60 user). The 1.50 user must own a 1.50 firmware PSP and will have to follow simple steps to obtain some files for you. The instructions are as follow - Before downgrading, make sure you meet the following requirements - Your PSP is not a TA-082 (If you do have this PSP version, it may result in a brick) You do not have a factory 2.5/2.60 PSP (DG only works on updated PSP's) 1.50 User Instructions 1. Copy the folders downhelper and downhelper% from the folder 1.50 HELPER folder to /PSP/GAME/ in your memstick. 2. Obtain the 1.50 update and put it in /PSP/GAME/UPDATE in your memstick. You may find the 1.50 update in our download site here. 3. Init the downhelper program. 4. It will dump your flash and some files from the updater eboot to the memstick. (These files are illegal under US copyright laws, so please do not distribute them in the comments or on our forums) 5. After that, the program will exit. You can now delete the updater from /PSP/GAME/UPDATE 6. You'll notice that you have a new folder in the root of your memstick called "DOWNDATER". 7. That's the folder you'll have to send to a 2.50/2.60 to let him test the downgrade. 2.50/2.60 User Instructions 1. Copy the folder the DOWNGRADER/2.50/DOWNDATERTEST if you have 2.50 2. or DOWNGRADER/2.60/DOWNDATERTEST if you have 2.60 to /PSP/GAME/ in your memstick 3. Wait for someone with 1.50 to pass you a folder called DOWNDATER and copy it to the root of your memstick. 4. Init GTA and the eLoader 5. In the eLoader menu, choose the downdater test. WARNING: the program won't output any display and any warnings, it will init the downgrader process inmediatelly. 6. You'll see the your memstick flashing. That means that your psp is being flashed from the memstick. 7. You won't see any type of output in the screen (this is for safety). When the memstick finishes of flashing, WAIT at least a minute, and then reinit your psp by holding the power button. 8. That's all. If all went right, you'll have 1.50. If it went less good, you'll still have 2.50/2.60. If all went wrong, you'll have a bricked psp(except in the case you have the modchip) Remember that you have accepted that risk.

虽然还是测试版的，但是国内的许多玩儿架成功了。但是需要注意的几点是：
需要降级的PSP的主板不能是：TA-082。
而且不能是从其他的版本升级上来的。
否则的话，您又会为长城添加一块儿SONY牌的板砖>_<

以下是降级程序的下载链接：
2.6
http://dl.qj.net/downdater-2.60-%28downgrader%29-v5-beta-psp-homebrew-applications/pg/12/fid/8540/catid/151
2.5
http://dl.qj.net/2.50-downdater-%28downgrader%29-v5-beta-psp-homebrew-applications/pg/12/fid/8539/catid/151
1.5 downhelper
http://dl.qj.net/1.50-helper-%282.5-2.6-downgrader-helper%29-psp-homebrew-applications/pg/12/fid/8541/catid/151

文件解压密码：I_USE_AT_MY_OWN_RISKS
附fm1.5 的dump文件：
http://www.svsu.edu/~mcmcelro/freeplay/26dg/

个人没有PSP，所以也就没有机会尝试了，更没有机会为长城做贡献了。
看看其他的帖子，好像这个消息出来已经很久了。
火星的话，就别BS我了，本来就很没面子了~~

……好象现在1.5能模拟2.5的……吧