Do you mean that you want to do this in a bulleted list? If so, under
format, bullets and numbering, choose the alpha style (upper or lower) from
the numbers tab. Then change the "start at" number to be 28 and the letters
will start with ab, ac, ad etc. In HTML/Code View it would look like:
<ol style="list-style-type: lower-alpha" type="a" start="28">
<li> </li>
</ol>
If you didn't mean in a bulleted list please give more details.