Not much changed on the Billboard magazine pop chart over the holidays. Albums by pop-rappers Vanilla Ice, "To the Extreme" (No. 1), and M.C. Hammer, "Please Hammer Don't Hurt 'Em" (No. 2), continued to rule the chart. The Simpsons don't have any reason to sing the blues. Their novelty album, "The Simpsons Sing the Blues," was one of the most popular new albums during the holidays, sprinting up to No. 7. The Led Zeppelin retrospective package, retailing for around $55, is still selling big. After 10 weeks on the chart, it's No. 22, slipping just a notch. Madonna's "Justify My Love" continues to top the pop singles chart.