다음 팁앤테크 참고하십시오.
http://www.sir.co.kr/?doc=bbs/gnuboard.php&bo_table=tiptech&wr_id=6560
적용URL
http://threes.org/gnu3/?doc=main_boardsearch.php

<form name=fsearch method=get action='./'>
<input type=hidden name=doc value='bbs/gnuboard.php'>
<input type=hidden name=bo_table value='qa'>

<input type=hidden name=ca_id value=''>
<td width=50% align=right valign=bottom>
<select name=sselect>
<option value='concat(wr_subject,wr_content)'>제목+내용</option>
<option value='wr_name'>이름</option>
<option value='wr_num'>번호</option>
<option value='wr_datetime'>날짜</option>

<option value='wr_subject'>제목</option>
<option value='wr_content'>내용</option>
<option value='wr_hit'>읽음</option>
</select>
<input type=text name=stext size=10 required itemname='검색어' value=''>
<select name=soperator>
<option value='0'>OR</option>

<option value='1'>AND</option>
</select>
<input type=image src='bbs/skin/board/basic/search.gif' border=0 alt='검색' align=absmiddle>
</td>
</form>



여기서 <input type=hidden name=bo_table value='qa'> 만 원하는 게시판 아이디로 수정하면 되겠군요.