Well, it may. An undergraduate degree from an elite institution like Harvard will certainly boost your application, but it will not necessarily guarantee you admission. You would still need excellent academics and good research/work experience to be able to make it to top universities for graduate school. Of course, if two students present similar statistics, but one graduated from an Ivy League university, they will certainly be held at higher ground than the other. In short, the prestige of your undergraduate institution might matter, but it will always be secondary to your GRE scores, GPA, and research/work experience.