The man who tried to shake down David Letterman over his affairs with members of his staff will be going to jail for six months as part of a plea deal.In entering a guilty plea today, Joe Halderman admitted that he tried to extort $2 million from Letterman by threatening to disclose information about him.Halderman's lawyers initially said he was just offering to sell letterman a screenplay about the comedian's life.If he'd been convicted at a trial, Halderman could have faced up to 15 years behind bars.