By "free windows" do you just mean an unactivated copy of Windows? That doesn't prevent the user from configuring their preference in the browser itself.

There should be a button too, but it's simple to add a line so that it also defaults to any provided preference.

That's fine, too. Either way, give the user the choice.

… is that even legal to do for microsoft? Are there no requirements to adhere to certain standards? Would have thought that is part of it.