The BBC has a useful piece on US preparations for cyberwar, Meet USCybercom: Why the US is fielding a cyber army. All four armed services have created single units for cyber operations under the USCYBERCOM umbrella: 24th Air Force, 10th Fleet, and Marine Corps Cyberspace Command are all operational. The US Army Forces Cyber Command is a little behind, but may be activated by October 2010. For an idea of how the US Army views its role in this operational environment, check out its new Cyberspace Operations Concept Capability Plan, 2016-2028 (February 2010, pdf).
US Cyber Command itself is waiting for Senate confirmation of LTG Keith Alexander, currently head of the National Security Agency (NSA) and Chief of the National Security Service (NSS), as head of the command. Given his likely appointment soon, and budgetary approval, USCYBERCOM will be ready to roll.
I recommend reading through the article, as it sets out from interviews the rationale behind the creation of this new command. Also, the single best source on the web for information regarding this topic is Bruce Carleton’s USCYBERCOM Watch. Active since last October, Bruce has kept an eagle and dispassionate eye on developments in this field, and is essential reading for anyone interested in how a massive organisation like the US military creaks and groans as it reorients and reorganises to operate in cyberspace. It’s actually quite striking how quickly it is managing to do this, despite the bureaucratic and fiscal constraints upon it.
Update, 17 March: There’s more info on the preparations for US Cyber Command at defpro.news.