It sounds like to me that you already have your own CFW Psp. All you need to do is get
TOTALNewbi-esayInstaller
Then just follow the on screen (computer screen that is) Instructions to make your Magic memory stick. After you make your magic memory stick, put it in your CFW psp and run the pandora's battery maker on your friends battery.
BTW.. I would use the one that installs 3.71m33 for you otherwise your going to have to find the 3.5m33 upgrade and then jump to 3.9m33_3 which is more of a pain because you have to find all the 3.5 files and all that stuff.
Okay so after you do all that watch the vid below which should explain the rest.
http://youtube.com/watch?v=Ik7SocRvJLU
Then after your completly done after you have installed 3.90m33_3 run the memory stick on your psp again with the ac adapter and after its started up pop in the pandoras battery and run the pandoras battery creater again to change it back to a regular battery.