I work at a smallish (~125 employees) company and I'm lead of the test team. We have not had any college students interns in my test team. However, we've had high school students work over the summer and a junior team member with no formal test experience. Given their limited hours and/or experience, I believe some of my experience may work for you.
First and foremost, as if you didn't know, keep the tasks small. We have our best results when the assigned tasks were no more than a week in duration.
For example, we provide computer images to one of our customers that need to be validated. The validation of new images is fairly straight-forward, simple, and only takes one working day or less. Having the intern or junior member do this provides them the opportunity to quickly contribute useful results and get needed experience with our products.
So, find small, well defined tasks in your organization and assign them to the intern. You can also break larger tasks up into bite-sized portions.
Second, be sure the tasks are not high priority or needed on an aggressive schedule. The intern will likely take twice as much time as you think due to inexperience.
Third, identify one of your top testers and assign them as a mentor. However, be very careful of your selection. The mentor must be someone with excellent communication skills and an organized member of your team. Just because the person is a good tester doesn't mean they can train an intern to test or properly put the interns skills to good use. By putting the intern with someone who can easily communicate the needs and organized enough to assign appropriate tasks, they can quickly become contributing members of the organization.
I'll easily admit this was one of my downfalls with the high school interns. I was not the greatest at communicating what I expected of them and compounded the problem by not following up often enough. So, some of the tasks I assigned took longer than necessary and did not result in everything I wanted. Lesson learned, be clear, be concise, and follow up as needed.
Anyway, I hope these comments and suggestions help.