Well, it will depend in part on what game engine the developer is using. For music, most of the time it is streamed from the disc in ATRAC3 or ATRAC3Plus format. Sound Forge can convert to ATRAC3, but to get ATRAC3Plus you'll need the Sony Developer Tools I think...(at3tool).
Apart from that, some engines will convert the WAV files into ADPCM at runtime for the PSP, so you may not need to actually 'port' them.
Jamey probably has some additional info on this - he's worked on the PSP longer than I have.