Here is what I used and it seems to work ok. You can play around with the variables for the number of days to look back for with the username.
Code:
<table width="100%">
<td align="right">
<form method="get" action="search.php" name="">
<smallfont>Search by Username</smallfont>
<input type="text" name="searchuser" value="$searchuser">
<input type="submit" name="Submit" value="Go">
<input type="hidden" name="forumchoice" value="$forumid">
<input type="hidden" name="searchdate" value="1">
<input type="hidden" name="getdaily" value="yes">
<input type="hidden" name="action" value="dosearch">
<smallfont><A HREF="http://www.hometheaterforum.com/htforum/search.php?getdaily=yes&action=dosearch&searchdate=1&forumchoice=$forumid">
View Posts Over Last 24 Hours</A></smallfont>
</form>
</td>
</table>