What can this European court do if MicroSoft chooses not to comply? I don't see how they can realistically make Windows illegal in the European Union by court mandate.
They can impose hefty fines.
If Microsoft wins the lawsuit, it's likely that the next lawsuit will be against Samba, which allows Linux and Windows computers to share files, printers, etc. Microsoft doesn't want to allow their customers to do that.
Still, with that in mind, I don't see what forces MicroSoft to pay. I mean, what is Europe going to do? Ban the import of Windows?