Responding to a letter Microsoft sent the Yahoo Board of Directors over the weekend, Yahoo said not only is the offer not enough, threats aren’t going to get Microsoft anywhere.Steve’s letter said that Yahoo’s management is “choosing not to enter into substantive negotiations” with the Redmonds, letting “this window of opportunity” to reach a friendly agreement pass. If it has to come to a proxy fight with dueling director slates, it will be with a new offer as a backdrop—and it will be lower then the one currently