Instructions
Turn off the PSP and remove its battery. Reinsert the battery. Hold the "Right" trigger on the PSP and turn it back on. The recovery menu will appear.
Select "Plugins" from the PSP recovery menu and select the "Popsloader" plugin once so that it reads "Enabled" next to it.
Select "Back" and "Exit" to reboot the PSP. Popsloader is now enabled. Connect your PSP to your computer with the USB cable.
Click the "Start" button and "Computer" to open a list of drives on your computer. Open the "PSP" drive. Open the "PSP" folder on the PSP memory stick. You will see the "GAME" folder. This is where your PS1 games will go.
Drag your PS1 eboot files into the "GAME" folder in the PSP memory stick. Press the "O" button to disconnect the PSP from the computer. Select the game from the PSP menu's game section to play.