大家帮帮忙，帮我看看这段代码好么，多谢拉

这段代码能不能帮我看看，它的功能是图片点击后放大，为什么它现在直接显示图片原大
<table width="100%" height="313" border="0" cellpadding="0" cellspacing="0">
<tr>
<td align="center" valign="middle"><img src="images/common/none.gif" file="./upload/$pic" onclick="zoom(this, this.src)" id="aimg_3033" onmouseover="showMenu(this.id, false, 2)" alt="$tname" /></td>
</tr>
</table>
</div>
<script type="text/javascript" reload="1">aimgcount[28698] = [3033];attachimgshow(28698);</script>
<script type="text/javascript">
var showimg = new Image();
showimg.src = './upload/200904271932595.jpg';
function ImgWH(){
if (showimg.width > 250){document.getElementById("aimg_3033").style.width="250px";}
if (showimg.height > 313){document.getElementById("aimg_3033").style.height="313px";}
}
window.setInterval("ImgWH()",1);
</script>