Heat oven to 350 degrees F.
In a pot of simmering water, poach kielbasa for 20 minutes. Remove from pot; transfer to a roasting pan with about 1 cup poaching water. Using a fork, poke the skin of kielbasa to prevent it from cracking. Roast until brown and crispy, about 20 minutes.
Slice kielbasa on the diagonal into 1/2-inch slices. Serve with rye bread, horseradish, and mustard.
(c)2003 Martha Stewart Living Omnimedia, Inc. All Rights Reserved.