Getting Nth value with Linq
var nthItem = items.Skip(n).First();
You can use skip and take.
var result = myData.OrderBy(<your order by>).Skip(5).Take(1);
An alternative (.Net 3.5 and later) is to use ElementAtOrDefault.
var nthItem = items.ElementAtOrDefault(n-1);
The method's index is zero-based, so if you want the third element, you pass 2 for the index.