eww downgrading, you noob.

Go to psp-hacks.com, go to their forums, browse around the stickies, if you still cant do it, go to their IRC.
I simply uploaded a file to my memory stick, used a hacked PSP to make a pandoras battery and magic memory stick, then put the mem stick + battery into my slim (works with phat), held the R trigger and began the install.

Nice and easy.