Well, like I said, flats happen to everbody, so I still wouldn't necessarily blame your weight, but wider tires do lower the risk as far as I know. In regards to what tires fit on your rims, it depends on the width of the interior sides of the rims, and is a bit complicated; here's a chart that shows what fits (under "Width Considerations"), although you don't necessarily have to follow it religiously: http://sheldonbrown.com/tire-sizing.html

In general in regards to your question: the 700 is metric and refers to the diameter of the wheel in millimetres, the 32c is also metric and refers to the width of the tire (not the rim) in millimetres.

btw. there an extra forum dedicated to heavy cyclists here http://www.bikeforums.net/forumdispl...00-lb-91-kg%29