It's required for a lot of homebrew apps and most emulators. Here's how to install it.
1) Put
150.pbp in the root of your memory card.
2) Put this
UPDATE folder inside /PSP/GAME/
3) Make sure your kernel mode is set to 3.90 in the recovery menu, then run the updater from the game menu. If you didn't fiddle with the recovery menu, chances are you're already set, so just run the "updater".
4) When the updater finishes, let it reboot by itself, don't do it yourself.
5) Your emulators, ie Daedelus should now work.