I am using tables semantically by
- classifying them according to table type, then
- using CSS rules (Prince.css for printed output of course) to style the table according to its classification.

<table class="tableGeneral">
    <thead>
        <tr>
            <td>It allows ..</td>
            <td>To do this ...</td>
        </tr>
    </thead>
    <tbody>
        <tr>
            <td>Administrators</td>
            <td>
            <ul>
                <li>develop a project plan for the documentation project</li>
                <li>assign work, and</li>
                <li>follow the progress of the project.</li>
            </ul>
            </td>
        </tr>
        <tr>
            <td>Authors</td>
            <td>
            <ul>
                <li>identify topics</li>
                <li>organize topics into topic worksheets</li>
                <li>create and modify Maps and Blocks</li>
                <li>organize Maps into outlines, and</li>
                <li>generate publications.</li>
            </ul>
            </td>
        </tr>
    </tbody>
</table>

Is this markup ok, or should I be using <th> tags rather than <td> tags in the table header row?

In general th tags should be used for table header cells, although in practice this only matters when producing HTML content that will be published online, to benefit screen readers and other accessibility tools. For Prince it's not so important.

Okay, thank-you...