upgrading a slim 3.90 official firmware to 3.90 m33 custom

Gameboot: A 2.5 second video clip that flashes on the screen when you select a execute a game or application under 'GAME' in the XMB.

Cintro: Up to a 1:15 video clip that plays on your psp when you first turn it on.

Once you rip the ISO file to your computer, you can compress it to a .CSO file to make it smaller, and also rip some files off it using 'UMDGen v4'.
Then copy/paste the ISO/CSO file into the 'ISO' folder on the base of your memory stick.

Gameboot: A 2.5 second video clip that flashes on the screen when you select a execute a game or application under 'GAME' in the XMB.

Cintro: Up to a 1:15 video clip that plays on your psp when you first turn it on.

Once you rip the ISO file to your computer, you can compress it to a .CSO file to make it smaller, and also rip some files off it using 'UMDGen v4'.
Then copy/paste the ISO/CSO file into the 'ISO' folder on the base of your memory stick.

so as long as you put the iso/cso into the iso folder it will boot with no problems? no eloaders needed or any thing? Sounds too good to be true ;p

That's right .