- Download the TotalNewbieEasyInstaller program (Google or Yahoo! it).
- Run the program (Start.exe).
- Put your PSP (with the Memory Stick) into USB mode and connect it to your PC via a USB cable.
- Follow the instructions (this will involve formatting your MS stick so be sure to backup any content before).
- Choose 4. Universal Unbricker: 3.71 M33 Installer and install.
- Follow the instructions.
The next step is so easy even George Bush can do it:
- Make sure the Memory Stick is inserted inside.
- Insert the Pandora's Battery or Datel Tool battery into your PSP Slim's battery slot.
- Follow the instructions. Here you can restore your PSP Slim to 3.71 official firmware, install 3.71 M33 or backup the PSP's NAND ROM to MS by pressing 'Square'.
- Press 'X' to install 3.71 M33 firmware.
- Once done, remove the battery and insert a none-hacked battery.
- Turn it on. You can confirm the firmware by checking the System Information.
If you want to install the latest 3.90 M33, just download the M33 release file and Sony's official 3.90 update file and rename it to 390.PBP. Copy the UPDATE folder into ms0:/PSP/GAME and copy 390.PBP into the same folder. Navigate to GAME/Memory Stick on the XMB and run the installer. The firmware will be installed by Sony's own updater program. Make sure your battery is charged and follow the instructions. If you have a slow Memory Stick, you may want to patch the firmware with 3.71 fatmsmod.
After installing the custom firmware the first thing I recommend is to turn on your PSP while pressing the right shoulder button to put the PSP into recovery mode and "overclock" your PSP Slim into 333Mhz for games. This will provide a massive performance improvements to games originally developed to run at 222Mhz. Format the Memory Stick if you need the extra space.
After that how you want to use your PSP is up to you. I personally use it to extract the ISO from my UMDs so as to be able to run them from the Memory Stick rather than UMD drive. This is as easy as dragging the ISO onto your desktop, then compressing it via a CSO compressor utility (search engines are your friends) to reduce the size. The massive battery improvement alone is worth it, but there are other advantages like reduced loading time and the convenience of not having to carry many UMDs. I also use custom firmware to run PS1 games via emulation.
Disclaimer: This is merely a guide. I will not take responsibility if you brick your PSP.
Update: Not all PSP-2000 can be used with a Pandora battery, right now specifically those with TA-088 motherboards.