Well first off Welcome to AcidMods.
Tomrem is right, there is the adapter to use for added storage.
As for using the solid state drive, it can't be done and has been thought of many times over.
To interface it with the standard umd connections is just wayyyyyy too hard to do.
Slapping in any drive and using adapters won't work either, because both the psp and drive are slave, and would need some sort of bridge.