cabbage - volume to weight conversion?
A medium-sized cabbage weighs around 2 to 2.5 pounds. (Assuming we all mean the same thing by "medium"...) I think you'll probably be better off guessing based on fraction of your whole cabbage than volume, since once you shred the cabbage, the volume's going to vary wildly depending on how fine you shred it and how fluffed up it is when you measure it. My best guess for volume would be 10-12 cups.

Of course, you can always go to the fallback and find something else in your kitchen that weighs a pound (I tend to have pasta) and try and lop off a hunk of your cabbage that weighs the same.

Edit: I did find something on about.com suggesting that a medium cabbage is two pounds. Unfortunately it claims that a two-pound head of cabbage makes 10 cups shredded, but that a medium head makes four cups. I think the ten cups is way, way closer to correct, based on experience. If you do want a volume, that would probably be a good estimate.