在CSDN的论坛上一个朋友发的，转到这里以便用的时候直接copy和modify，省得自己写了。

function ubb2html($content)
{
global $article;
//是否自动识别
if ($article['isparseurl'] == "1")
{
$content = parseurl($content);
}
//自动识别结束

$content = eregi_replace(quotemeta("[b]"),quotemeta("<b>"),$content);
$content = eregi_replace(quotemeta("[/b]"),quotemeta("</b>"),$content);
$content = eregi_replace(quotemeta("[i]"),quotemeta("<i>"),$content);
$content = eregi_replace(quotemeta("[/i]"),quotemeta("</i>"),$content);
$content = eregi_replace(quotemeta("[u]"),quotemeta("<u>"),$content);
$content = eregi_replace(quotemeta("[/u]"),quotemeta("</u>"),$content);
$content = eregi_replace(quotemeta("[center]"),quotemeta("<center>"),$content);
$content = eregi_replace(quotemeta("[/center]"),quotemeta("</center>"),$content);

$content = eregi_replace(quotemeta("[quote]"),quotemeta("<table width="96%" border="0" cellspacing="3" cellpadding="0" style=word-break:break-all align="center"><tr><td><b>引用:</b></td></tr><tr><td><hr width="100%" noshade></td></tr><tr><td class="content"><font color="#0000FF">"),$content);
$content = eregi_replace(quotemeta("[/quote]"),quotemeta("</font></td></tr><tr><td><hr width="100%" noshade></td></tr></table>"),$content);

$content = eregi_replace(quotemeta("[code]"),quotemeta("<table width="96%" border="0" cellspacing="3" cellpadding="0" style=word-break:break-all align="center"><tr><td><b>代码:</b></td></tr><tr><td><hr width="100%" noshade></td></tr><tr><td class="code"><font color="#0000FF">"),$content);
$content = eregi_replace(quotemeta("[/code]"),quotemeta("</font></td></tr><tr><td><hr width="100%" noshade></td></tr></table>"),$content);

$content = eregi_replace("\[images\]([^\[]*)\[/images\]","<a href="\1" target="_blank"><img src="\1" border=0 onload="javascript:if(this.width>screen.width-333)this.width=screen.width-333" title="用新窗口浏览原始图片"></a>",$content);
 
$content = eregi_replace("\[url\]www.([^\[]*)\[/url\]", "<a href="http://www.\1" target=_blank>www.\1</a>",$content);
$content = eregi_replace("\[url\]([^\[]*)\[/url\]","<a href="\1" target=_blank>\1</a>",$content);
$content = eregi_replace("\[url=([^\[]*)\]([^\[]*)\[/url\]","<a href="\1" target=_blank>\2</a>",$content);
$content = eregi_replace("\[email\]([^\[]*)\[/email\]", "<a href="mailto:\1">\1</a>",$content);

//$content = preg_replace( '/javascript/i', 'java script', $content);
return $content;
}