If you don't want to deal with a car rental, there's Super Shuttle that'll take you from DIA to anywhere you need to go in Fort Collins, including CSU's campus. I haven't taken it for several years but I remember the price being fairly reasonable and it wasn't too big of a hassle. I would check out the site if I were you. The Super Shuttle would take almost two hours, but typically driving should take only about an hour if you take the toll (I took E470 and then I-25 and sped which cuts down on time 🙂 ).