Combine sugar and water in a medium saucepan. Make a simple syrup by bringing to a boil, then simmering 5 minutes. Add cranberries. Stir over medium heat about 20 minutes, or until all berries burst. Remove from heat. Add marmalade, lemon juice and walnuts. Stir to combine. Cool. Transfer to a serving bowl. Cover and chill thoroughly. Serve chilled.