According to Kotaku, Sony is planning to release PSP titles “remastered” for HD, similar to the PS2 titles like God of War and Sly Cooper. No word when this will happen yet in the U.S., but I’m sure we’ll hear about it at E3. The first title of the “PlayStation Portable Remaster Series” to hit Japan this Summer is Monster Hunter Portable 3rd. Gamers that have the game on PSP will be able to use their current save games on these HD remastered games and go back and forth between the versions, and multiplayer will work as well. Not only that, but there will be other add ons like exclusive new content.
Kotaku has a video showing the difference in between the PSP and the HD version: