Bethesda has already revealed some tidbits for their upcoming Fallout 3 "Mothership Zeta" DLC.  We know so far there are new weapons like the Alien Atomizer, Alien Disintegrator, and Drone Cannon to help you battle extraterrestrial forces, and new armor -- including Samurai gear.

Today, they've come out with new screenshots, and Bethesda's Jeff Gardiner mentioned a few more details to MTV.  The Alien Atomizer, we learn, is going to be a pistol, and the Disintegrator, a new rifle.

"Mothership Zeta is full of the most high tech weaponry in the game. It includes a Shock Baton for melee fighters, multiple new firearms including an Alien Atomizer, a pistol, and the Alien Disintegrator, a new rifle. There's also a new grenade type, a Cryo Grenade, which freezes enemies for a short period of time. On top of that there are new unique weapons, and a new heavy weapon."

A new unlock called "Xenotech Expert" will also boost the damage you do with alien weapons, like the Alien Blaster found in the wasteland.  This particular bonus is going to be mission-specific, since the "Mothership Zeta" DLC doesn't raise the level cap.

Additionally, you can head back to the ship even after you've beaten the main quest.  Might be a good idea, in case you want that special item called "Alien Epoxy," which can automatically repair an item by 25 percent even without a duplicate.