Table Headers spanning multiple columns

Good evening:

I am trying to get the header cells to span both columns on the table
below. I tried adding colspan='2' to both the cell and the row but
didn't work. I have looked at the html table sample in the docbook
guide but am having a really hard time understanding it.  Any and all
help is appreciated

Carlos

		<sect2 id="system-used-to-deliver">
			<title>
				Systems used to deliver synchronous Distance Learning
			</title>
			<table xml:id="question7" rules="all" frame="box">
				<caption>
					Systems used to deliver synchronous Distance
					Learning
				</caption>
				<thead>
					<tr>
						<td>
							7. What system(s) do you use for delivering synchronous
distance learning instruction? (Select all that apply.)
						</td>
						<td></td>
					</tr>
				</thead>
				<tbody>
					<tr>
						<td>
							Acrobat Connect Professional
							<sbr />
							(formerly Macromedia Breeze)
						</td>
						<td>Wimba Live Classroom</td>
					</tr>
					<tr>
						<td>Elluminate Live</td>
						<td>Centra</td>
					</tr>
					<tr>
						<td>Webex</td>
						<td></td>
					</tr>
				</tbody>
			</table>
			<para></para>
		</sect2>


-- 
Carlos E. Araya
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