Starting February 23rd, you'll be able to get your hands on Metal Slug XX, an updated port of Metal Slug 7 (Japan) being released in the U.S. for the PSP. Two-player ad hoc (wireless LAN) co-op is promised, as well as additional challenge missions and unique playable characters.
Metal Slug XX will be available on the PlayStation Network for download, and - presumably - in retail stores. [UPDATE - Just caught the price in the official press release, which Colony of Gamers has posted: $19.99] Check out the trailer below for a trip back to the Golden Age of shoot-em-ups.
Source: Blog.us.playstation.com