you need to look in your template folder and open up general.css and look for the code below.
.disignBoxFirst
{
position:relative;
background-image:url(../images/bottom_right.gif);
background-repeat:no-repeat;
background-position: right bottom;
margin-bottom: 10px;
padding-bottom: 25px;
}
.disignBoxFirst1
{
position:relative;
background-image:url(../images/bottom_left.gif);
background-repeat:no-repeat;
background-position: left bottom;
}
.boxFirstHeader
{
height:25px;
font-size:12px;
font-weight:bold;
color:#FFFFFF;
text-transform:uppercase;
background-image: url(../images/top_right.gif);
background-repeat: no-repeat;
background-position: right top;
line-height: 25px;
text-indent: 10px;
text-align: left;
}
.boxFirstHeader1
{
height:25px;
font-size:12px;
font-weight:bold;
color:#FFFFFF;
text-transform:uppercase;
background-image: url(../images/top_left.gif);
background-repeat: no-repeat;
background-position: left top;
line-height: 25px;
text-indent: 10px;
text-align: left;
}
of course you would need to make each image for the corners. but that should point you in the general direction.