Kristin,
From what I've read, CFRD is a combination of Type I and Type II. As Jen said, we may make less insulin, but our bodies may ignore some of our insulin as well due to the constant state of infection.
The idea is if your pancreas is affected by CF (making you pancreatic insufficient), over time there will be scarring (fibrosis) in your pancrease which will diminish your pancreas' ability to make insulin.
At least that's what I've heard...
Kris