[bah]

ISOs are files that are an 'image' of the contents of a disc.

What a rom (like a SNES game rom) is to a cartridge, an ISO is to a disc.

On the PSP, ISOs generally refer to pirated PSP games that people play from their memory sticks.

I don't agree with their use, piracy is rampant and the PSP has poor enough games sales as it is. If games don't sell, then developers wont bother making new ones for the system.
If people were just dumping their own UMDs to reduce load times I wouldnt mind, but most people (im not saying you) who ask about loading ISOs have no intention of buying the game.

For those reasons I don't provide any help on ISOs, theres sure to be others who will on this or other forums.