At 375lbs I have to strongly recommend talking to your doctor before launching into C25k. When running, every pound on your body is equivalent to 5 pounds of force on your knees every time your foot falls. You'll also be putting a massive burden on your heart. Go to the doc and get as many assessments done as your insurance will cover.

I say this out of concern, and not in any way trying to discourage you. I absolutely feel you should pursue your dream, just as safely possible.

As others have said, invest in your shoes. Go one step further than this - get a consult with a pedorthist and check how you distribute your weight. I had horrific knee problems when I started (and that was at only 200lbs) and a doctor recommended visit to the New Balance pedorthist showed that I supinate horribly, and have ludicrously high arches. A new pair of shoes + wedge inserts + arch supports and my knee issues all but disappeared. 20lbs of weight loss later, and I feel like I have new knees. Short cut the whole process, and assume up front that you are probably going to have knee problems. Especially since the pedorthist consult is free.