the iriver should have a cable that you can use I think, if its got OTG support then yes you should be able to. I would check more into the OTG spec for the h320 with iriver (fire off a quick email) My otg device uses either a standard A to mini B cable or a mini A to A extension socket so I guess to connect to the PSP u would need both types of cable.
Going something like this: PSP<mini B----A><A Extension-------mini A>H320
You are basically turning ur Iriver into a PC (as far as the USB host/client side of things goes). But check with Iriver, it could be that you can use a Mini A to Mini A but I doubt it unless the iriver has some funky circuitry to flip a couple of wires.