Capcom just posted this on its site:
http://www.capcom.co.jp/monsterhunter/3/
a brief Google translation:
Some in the magazine article, "Monster Hunter 3 (tri) to expand outside of the Wii" Thank you very reports, the Company announced that in all, and does not go.
The latest film Monster Hunter Series 3 (tri)'s, Wii advantage of the characteristics of the unprecedented ensure the creation of a monster hunter, is keen to develop.
So no PSP version, but a new Monster Hunter Portable is inevitable