From Gizmodo :

The Zunes will be brown with fancy Halo artwork and will come pre-loaded with artwork, trailers, and music from all three Halo games. No word on whether or not this Military exclusive will sell to soldiers for any cheaper than the standard pricepoint of $250.

Unfortunately there are no more photos available of this new Halo 3 Brown Zune. Check below for more information about the previously released Halo 3 Black Zune. 

EDIT: the full announcement, via teamxbox :

Microsoft Brings Zune - Halo 3 Military Edition to Service Men and Women

On the heels of the popular black Zune – Halo 3 Edition, Microsoft is introducing a new brown version of the Halo-themed player for military service members. After receiving feedback on the popularity of the Zune players from U.S. soldiers, teams from Microsoft Zune and Microsoft’s U.S. Federal business joined together to develop a special Zune – Halo 3 Military Edition, which will be available exclusively at military retail stores in August. The new version of the Zune – Halo 3 Edition player will be packaged in a collectible Halo 3 box, and will come pre-loaded with artwork, trailers, and music from all three Halo games.

A group of soldiers leaving for active duty from the Baltimore Washington International airport on August 6th will be the first to receive the new Halo Zune devices. Working closely with the USO, a non-profit organization focused on improving the quality of life of service members, Microsoft contributed 300 of the new Zune players to the USO of Metropolitan Washington to be part of a special USO care package the soldiers will receive. While visiting the USO lounge at BWI, soldiers can use the Windows PCs at the lounge and a special Zune listening station to load their devices with additional content before their departure.

“Microsoft has been a great partner to the USO of Metropolitan Washington for several years, supporting both our U.S. soldiers and the USO’s mission,” says Elaine Rogers, president of the USO of Metropolitan Washington. “ From Zune devices and Xbox 360 gaming consoles to new computers with the latest Windows Vista and Office software, Microsoft’s technology has helped service members stay connected and entertained.”

Microsoft is offering the Zune – Halo 3 Military Edition to military personnel and their families at discounted rates through military retailers, including AAFES, and Navy and Marine Corps commissaries, beginning in early August. All versions of the Zune device have 30GB storage, a 3-inch screen that displays content in portrait or landscape mode, a built-in FM tuner, rugged exterior, and wireless capabilities that provide Zune-to-Zune sharing so users can exchange songs, playlists and photos with the click of a button.

Related articles:
Military Brown Halo 3 Zune on eBay
See all the preloaded Halo 3 Zune Photos (not sure if included in this new version)
Halo 3 Zune: 20000 pieces limited edition (With many more references)