Adding thousands of users easily from a text file

Hi all, i am running drupal 5.3 and have to add about 1500 users so they can login. The site is for my school yearbook class (link)..I have experiance with programming so i have made a java program that pulls the users name and student number from a text file provided from my school and can connect to a mysql database but i do not know how drupal's database is stuctered and how drupal adds a user. Is there already a module out there that does this kind of functionality? Thanks for your help :P