Valve has announced the release of a 2.5GB Warhammer 40,000: Dawn of War II demo, available to download exclusively through Steam.  The 333MB download allows players to sample the campaign mode of Relic's sci-fi strategy sequel. While many got a sneak peak at the game in the public multiplayer beta held prior to its February 19 release, campaign gameplay was not offered. In celebration of the demo, Steam--required to run the game--is offering a 25% off discount, bringing the game's cost down to $37.49. The sale ends Monday, April 20.