How do they do the sliding-in Google search box?

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On some sites (especially forum sites), I often see "search" and when I
click on it there is a Google search box/dialog which "slides" on.

I am using this code on my page:

<form method="get" action="http://www.google.com/search">
<div style="border:1px solid black;padding:4px;width:20em;">
<table border="0" cellpadding="0">
<tr>
<td>
<input type="text" name="q" size="25"
maxlength="255" value="" />
<input type="submit" value="Search" />
</td>
</tr>
<tr>
<td align="center" style="font-size:75%">
<input type="checkbox" name="sitesearch"
value="mysitewordhere.com" checked />
only search our site<br />
</td>
</tr>
</table>
</div>
</form>

How can I go about using a word (e.g. "search" or "find") so that when
someone clicks on it, the sliding search box opens up?