Born in Loveland, Colorado, Harstad led Thompson Valley High School to a conference championship during his junior year. In a decidedly Big 12 Conference region of the country, Harstad instead signed to play for Tony Barone at Creighton University, a Missouri Valley Conference school in Nebraska. When he enrolled a year later in the fall of 1987 he made an immediate impact for the Bluejays.
He averaged 9.0 points and 8.5 rebounds per game.
His rebounding average was the fourth best in National Collegiate Athletic Association Division I for freshmen. He started every single game—something he would do for his entire four-year career—as Creighton finished with a 16–16 overall record.
Over the next three seasons, Harstad guided the Bluejays to a very successful stretch in its program"s history, meanwhile earning personal accolades and setting still-standing records.
In his sophomore and senior years, Creighton won both the regular season and conference tournament championships en route to berths into the 1989 and 1991 National Collegiate Athletic Association Tournaments, respectively. The Bluejays managed to upset #6 New Mexico State before losing in the round of 32 during the 1991 tournament.
And, although the school failed to qualify for the National Collegiate Athletic Association Tournament in his junior year, they did get selected to play in the 1990 National Invitation Tournament.
That season, Harstad averaged a career-high 22.2 points and a second-best 8.8 rebounds per game. He was chosen as the Missouri Valley Conference Player of the Year, becoming the first player from Creighton to ever win the award. During his final three seasons he was named to the All-MVC First Team as well.
Harstad finished his collegiate career with 2,110 points and 1,126 rebounds, which as of 2011-2012 are both the second most in school history.
He is still one of just four players in conference history to finish with 2,000+ points and 1,000+ rebounds. Oscar Robertson, Xavier McDaniel, and Larry Bird also achieved this, and all three of them are in the Basketball Hall of Fame.
While not a member of the Basketball Hall of Fame himself, Harstad is a member of the Missouri Valley Conference and Creighton University Halls of Fame. His number 30 jersey was also retired by the school.