Instructions
Download PSX2PBP.
Open the PSX2PSP zip file and extract it to your desktop.
Run PSX2PSP.exe. Select "Classic Mode."
Click the button labeled "..." under "ISO/PBP File." This will open a file selection window. Use the file selection window to select the PBP file you wish to convert.
Click the "Extract ISO" button. Enter a name for the ISO file, then click "Save." PSX2PBP will extract the PSX ISO from the PBP. It will take approximately two minutes.