You're missing the <form> tags!

You are using form commands but not telling the code where to go.
Use this code:
Code:
<form action="search.php" method="post">
<input type="hidden" name="searchuser" value="">
<input type="text" name="query" class="search">
<input type="hidden" name="forumchoice" value="-1">
<input type="hidden" name="searchdate" value="-1">
<input type="hidden" name="sortby" value="lastpost">
<input type="hidden" name="sortorder" value="descending">
<input type="hidden" name="beforeafter" value="after">
<input type="hidden" name="action" value="simplesearch">
<input type="hidden" name="titleonly" value="">
<input type="hidden" name="showposts" value="">
<input type="hidden" name="exactname" value="yes">
<input type="submit" class="bginput" name="Submit" value="Search" accesskey="s">
</form>