Have you looked at NewEgg's source?
The HTML for each review entry looks like this:
<tr>
<td height="20" valign="top" class="BlackDescription">
<div id='CReview1_b' style='display:block;'>teaser...<a class='blue' href='javascript:Toggle("CReview1");Toggle("CReview1_b");' id='xCReview1'>See complete review></a></div>
<div id='CReview1' style='display:none;'>full article...</div>
<br><br>
</td>
</tr>
When you click the 'see complete review' link, the javascript toggles the first div (CReview1_b) from 'display: block' to 'display:none' and does the opposite for the other (CReview1).
The first div is merely the first X chars of the second div.
Those divs would be built server-side, in this case by ASP, but could just as easily be done with PHP using substr().