I did a truncated version of C25K earlier this year, in order to get back to exercise after injuries led to being scared to exercise which led to complete laziness etc.
It's a great course.
DO download the podcasts HERE
DO join the online support group HERE
I just did our local annual 10K yesterday (punching fists in the air smilie) - and that's after starting the Couchpotato to Runnerbean course in January
As to how much it will lower your BGs - only your meter will tell you that as it will be different for each person, dependent on starting BMI etc, BUT the main thing is - it will help with your BGs and will make you feel better and will help in a lot of different ways.
So - good luck with the C25K, and if I can help in any way just PM me