Here is my code but I dont know how to make is round corner,
{* $Id: dialog.tpl,v 1.19 2004/06/24 09:53:29 max Exp $ *}
{if $printable ne ''}
{include file="dialog_printable.tpl"}
{else}
<TABLE border="0" cellpadding="0" cellspacing="0" {$extra}>
<TR>
<TD height="15" class="DialogTitle" background="{$ImagesDir}/dialog_bg_n.gif" valign="bottom">{$title}</TD>
</TR>
<TR><TD class="DialogBorder"><TABLE border="0" cellpadding="10" cellspacing="1" width="100%">
<TR><TD class="DialogBox">{$content}
</TD></TR>
</TABLE></TD></TR>
</TABLE>
{/if}