BuddyTV - USA - FOX has announced its special musical guest for Thursday's So You Think You Can Dance live results show: Hillary Duff.  Duff, the singer/actress (Lizzy McGuire, Cheaper By the Dozen), will perform the the third single, Stranger, from her new album, entitled Dignity.  This is the second Thursday episode in a row that So You Think You Can Dance will have wrangled a major celebrity for its guest performance (last Thursday episode featured Fergie and Ludacris).  Duff's latest album has been somewhat of a disappointment in record sales, debuting at #3 on the Billboard charts, selling around 140,000 copies in its