The magical 2.0 PSP firmware—the version with a web browser, AVC/AAC support, and some graphics features like GIF support and image send and receive—is available on the Japanese PSP site and apparently works perfectly with US PSPs.
i4u has the skinny on installing the new firmware:
The EBOOT.PBP files needs to copied to the memory stick under the folder PSP/GAME/UPDATE After that try to access the memory stick from the menu. The PSP is then detecting the update. After confirming a license agreement the update process starts.