I need help on how to run psp iso/ homebrews. I just updated to 3.95, i have a older or "fat" psp. Is there anyway to run these games without buying or making one of those pandora batteries & the magic memory stick? If there isn't then how hard is it to make one? and when i downgrade to whatever version i need to run the homebrews will i be able to play movies and music still? I would appreciate it if anyone would help. thanks.

You need to buy or make one a Pandora's Battery, yes.
The Magic Memory Stick can be made on your PC: http://forums.afterdawn.com/thread_view.cfm/591203
It is quite hard to make the battery if you haven't got access to a PSP with custom firmware as you have to open up the battery (it should detail this in the above link).
If you downgrade and/or install custom firmware, you will still be able to play movies and music.

how much do the batteries usually cost?