Question: What is the best way to do a table of contents for an existing Word document?
Answer: The easiest way is to use heading styles for the topics you want in your document and then go to where you want to place your TOC and from references tab click Table of Contents and select a style and it will create one based on the heading styles. Super easy. There are also three step-by-step courses at Microsoft that are good too.
http://office.microsoft.com/en-us/training/word-2007-training-courses-HA010215566.aspx and scroll down to 4. Add finishing touches to your document