A new trailer introducing the Eldar campaign can be viewed below.
BOOM video 6593
Retribution is a standalone game in the Dawn of War II series and will not be backwards compatible with the original game or its expansion, Chaos Rising, due to Retribution's use of Steamworks over Games for Windows Live.
Retribution is planned for release in March of 2011. A beta, run through Steam, is planned for owners of Chaos Rising.