Here's the latest version. I'm going to call this 50% done.
Important change: This version is a form! You can enter your data and the form will do the math for you! I haven't had a chance (working 4 hours straight getting it to this point) to check the math. You are warned.
Let me know about any problems. I recommend Acrobat 5 for this version (and future versions).
[edit] New version below...