It's all done with images. If you look in the page source, this is what you will see for one of the posts (it's all one line because of what they have done to the source):
HTML Code:
<table cellSpacing="0" cellPadding="0" border="0" style="width:auto"> <tr> <td style="padding: 0px"><img src="images/quote/admin_01.gif"></td> <td style="padding: 0px" background="images/quote/admin_02.gif"></td> <td style="padding: 0px"><img src="images/quote/admin_03.gif"></td> </tr> <tr> <td valign="top" style="padding: 0px" background="images/quote/admin_04.gif"> <img src="images/quote/admin_05.gif"></td> <td style="padding: 0px; background-color: #ffffff" bgColor="#ffffff"> <div id="post_message_34705">mình th?́y Vi?̣t Hương r?́t năng n?̉ mu?́n chung tay x?y dựng di?̃n đang, đ?̀ng thời có kinh nghi?̣m làm mod, smod m?̣t s?́ trang, vì mu?́n BQT có th?m nữ giớ cho c?ng bằng và phát tri?̉n r?̣ng khắp mu?́n anh em vào cho ý ki?́n đ?̉ các admin xem sét c?́p mod cho Vi?̣t Hương</div> </td> <td style="padding: 0px" background="images/quote/admin_06.gif"></td> </tr> <tr> <td style="padding: 0px"><img src="images/quote/admin_07.gif"></td> <td style="padding: 0px" background="images/quote/admin_08.gif"></td> <td style="padding: 0px"><img src="images/quote/admin_09.gif"></td> </tr> </table>
You'd have to make all of the table go around the <div>message</div> part of your message.