As I read it, it's up to the States to see that the ruling is enforced, not the Federal Government.

From the [link|http://twiki.iwethey.org/twiki/bin/view/Main/DoJvMSFTFinalDecree#IV|twiki]:

IV. Compliance and Enforcement Procedures

A. Enforcement Authority

1. The Plaintiffs shall have exclusive responsibility for enforcing this Final Judgment. Without in any way limiting the sovereign enforcement authority of each of the plaintiff States, the plaintiff States shall form a committee to coordinate their enforcement of this Final Judgment. A plaintiff State shall take no action to enforce this Final Judgment without first consulting the plaintiff States' enforcement committee.

But, IANAL.

Cheers,
Scott.