trouble is that they probably just bought the sound files anyway.
I mean I doubt that microsoft employs a team of musicians on a permentant basis, hence they were probably freelancers using their own time and tools to create the sounds.
it's illegal to use pirate software, it's not illegal to listen to the results of that, and microsoft arn't directly profiting from the pirating of the software... the long and the short of it is that microsoft don't need to comment, or be investigated, or sued or anything... they are pretty much the innocent party in all of this...
besides which, think about it, bill gates could buy an entire music studio and employ musicians to make the background music for XP with his pocket change, why would he be ripping of a few hundred quids worth of software?
especially when they (as a company) could have probably profited from it themselves by writing off the tax as a business expense.