1public class DescendingComparer : IComparer
2{
3CaseInsensitiveComparer _comparer = new CaseInsensitiveComparer();
4public int Compare(object x, object y)
5{
6// Reversing the compared objects to

7// get descending comparisons

8return _comparer.Compare(y, x);
9}
10}

Ex. 
//Class
SortedList sort = new SortedList(new DescendingComparer());

//Method
coll.Sort(new DescendingComparer());