The idea is that you call QueueUserWorkItem once for each work item. How many work items have you got? 255, right? So you call QueueUserWorkItem 255 times:
vb.net Code:
  1. For i = 1 To 255
  2.     ThreadPool.QueueUserWorkItem(AddressOf SomeMethod, i)
  3. Next
In SomeMethod you get the value of i, make an IP address out of it and ping it. That is all you do. The system handles the rest.