They need to make a Legal definition of "Computer Operating System." Something simple. for instance, the Linux Kernel could be considered an operating system.

They must make this definition dynamic so it can be updated easily with time. But not too easy, we know how money and politics work.

Any company that develops a Computer Operating System for profit cannot develop code that extends beyond the scope of the legal definition.

Microsoft would, of course, be given a time frame for the implimentation of this business model. If they extend beyond this time frame, the government would have the right to step in and do the splitting themselves.