I can't see why Microsoft would bother pursuing people for downloading or seeding this. The cat is out of the bag. And people will use this in ways MS don't want regardless of what they do. It is not like a movie where there is a loss of hypothetical revenue. Source code is not exactly an easy was to install a pirated OS!

Plus it's not like someone's gonna run XP SP1 on their main machine. It's been 18 years.