This development has been out there almost a year ago but it was just recently that I discovered it and applied to my PSP. It temporarily loads a custom FW which means that the PSP will go back to the official FW once rebooted. After the reboot, the whole process needs to be re-done to reload the CFW. 

The process is a combination of the following: (1) loading ChickHen and (2) running CFW Enabler 3.60.

The first one (ChickHEN) allows us to play homebrew games on the PSP but not those games in ISO and CSO formats. Without ChickHEN, the CFW Enabler won't run in the PSP.

The second one (CFW Enabler) will load the custom firmware (CFW) MHU that allows ISO and CSO game formats to be played on the PSP.

Click here to see the step by step video guide on this.

BTW, this is a completely safe process, and there is NO WAY that any PSP will be bricked from trying this out, even those unhackable ones. On top of that, there is no OS requirement for the computer. It doesn't matter whether you have Windows Vista, XP or 7, or even a Mac, because everything will be done on the PSP. The computer is used only for transferring the files that need to be in the memory stick, no application will be run from the computer. 
See the top of this page for the download link for PSP games and movies to avoid buying expensive UMDs!