15K training & hill workouts

Hi everyone-
I am currently in training to run a 15K on September 6th, I have been using Hal Higdon's 15K training plan which I like a lot.
The course is on rolling hills (blacktop) and some of the hills are pretty steep.
Not sure the best way to prepare for this as how often I want to incorporate hill workouts into my training.

Anyone have any ideas?

Living in Louisiana we pretty much have no hills so hill training for me consists of running up and down a parking garage at a local college near my office.   If you have hills you may want to incorporate hill repeats into your training plan.   Hill repeats are running up your hill at race pace then walking or jogging down the hill to recover.  Rinse and repeat as needed.

What I do when I run my parking garage is I run up the 'hills' as fast as I can at race pace then I jog at a slow pace back down to the bottom.   I usually will do this twice in on of my 6 - 8 mile runs and three to four times when I run shorter distances. 

Like Chad said, just find a hill that represents an approximation of the race hill you are looking to conquor and run it 6-8 times.  I would do it once a week at most incorperated with your regular workouts.