Clarification:
To access the Index and Tables dialog box, select
Insert>Reference>Index and Tables (or simply Insert>Index and Tables
in Word 97 or 2000).
In the dialog box, click the Table of Contents tab. At Formats, select
"From template", and then click the Modify button. When you've made
your changes, click Apply to close the Style dialog box.
Close the Index and Tables dialog box by pressing the Cancel button.
Do *not* click OK, since this will create an additional TOC or replace
the current one, and neither of these options is a good one (for one
thing, it will result in a duplication of the bookmarks Word uses to
link to headings in a TOC).
If you are using styles and want to change the appearance of headings
in your document, modify the heading styles. Do *not* add the
formatting directly to text (for example, via the Font dialog box or
toolbar buttons), since this will reflect in the TOC entries.
For more about TOC creation, see
http://www.shaunakelly.com/word/toc/CreateATOC.html