The first part of the process is to set up a multilevel list and associate it with the heading styles in your document, if you haven't already done so. Follow the instructions in
http://shaunakelly.com/word/numberin...g20072010.html.
The second part is to modify the built-in styles named TOC 1 through TOC 9 so they have the indents you want, as shown in
http://shaunakelly.com/word/numberin...fcontents.html.