I decided that going to the people who actually write the code would be the best place to start.
What I'm needing is a way to use the PSP as a way to transfer hi res images from my CF card cards to a portable 2.5" Hard Drive, without using a laptop or desktop.
Is this possible?
If either the portable harddrive or the PSP have hardware USB on-the-go support then I don't see why it would be a problem.
Unfortunately, the PSP doesn't have a CF slot (nor are there handy CF->MS Duo converters). Also, the PSP doesn't act as a USB Host, nor does it supply power through the USB.
What you might want to look into is the Archos line of Personal Video Players, they range in 40GB-100GB, can act as a host, and many of them come with CF readers built-in, as well.
Only disadvantage is they're quite spendy. Here's the website.
Thanks JZT for the clarification. If the PSP doesn't support USB OTG (act as a USB host) then the hard-drive MUST support it. It's not something that can be hacked in software in most cases unfortunatelly.