For those who believe it's the hard way or the highway, several sites explain how to build whistles (mostly) from scratch:

• Erik Tolp-Olsen offers instructions on making a tin whistle. He explains how to calculate the length of tubing necessary to craft a whistle in a particular key and how to determine the position of the finger holes.
  
  
• Robert McElroy has contributed to the Chiff & Fipple Web site detailed (read: massive) instructions on building a tin whistle from copper tubing. This page contains a wealth of information, but it's not for fainthearted. The instructions are split into several parts: selecting the tubing, cutting the tubing, and drilling the finger holes.and connecting the mouth piece.
  
  
• The most impressive set of whistle-making instructions I've seen come from Kim Fulton-Bennett. Well organized, well written, and beautifully illustrated, these instructions will make you marvel at the amount of work that goes into creating a whistle and (if you're at all like me) convince you that only a lunatic would attempt to make one himself.
  
  
• Dennis Havlena aims to explain how to easily build a low D pennywhistle. Besides offering general building instructions, Dennis lists the exact dimensions (presumably for comparison purposes) of a copper and an aluminum whistle that he made. The ingenious ASCII illustrations alone are reason enough to check out his instructions. When you finish, swing by his home page, where he presents more instrument-building ideas and instructions.