i dont know how to play iso's on a official 3.40 FW. i know the custom but not official.. just need to know what to do so that i dont brick my friend's PSP

THANX!!!!

You cannot play ISOs on official firmware (except for 1.50).
You need to install custom firmware on his PSP.
The two main ways of doing this is via the 3.50 downgrader (you need an original Lumines UMD for this) or Pandora's Battery (it is preferable to have a PSP running custom firmware to do this).

Also, to play iso's on 1.50 OFW you need DevHook but updating to a CFW is better.

thanx for the help..... can i get further guides step by step?

so i need to have a lumines and download the downgrader right? then downgrade to 1.50 and after that install a OE firmwire and install the emulators? or am i missing something?

Yes, Lumines will work (only the first NOT the second one) or you could use Pandora's battery if you have a spare battery or someone with a PSP that has CFW on it but the Lumines method would probably be easier. You also have to download the CFW you want to update to which you can find here: http://www.dark-alex.org/ then install it, and your pretty much done. After that, install homebrew apps. and put ISO's on your memory stick and you're set.

thanx bro.... i had an idea but i didnt want to brick it like i did mine.. it seems like nobody has figured out a way to help me out. knight has helped but i cant still figure it out. my PSP turns on black but not totally, and i can still access recovery. i have used like 6 different recovery modes but none work. ive tryied upgrading to 3.90 M33(i have 3.80M33 on this PSP) and when i run it it says:

unpacking....done
390.PBP....does not exist
Do you want to download from the internet? (y or n)

and i click x and it just turns off man.....
i even check on the recovery and it says i can change on 3.90 and 1.50 kernel.