How do I add a BG image to my "boxes"? Options

[broKenhaloK]

I am using the following code for my xanga's entries boxes... I got it from a friend so I don't know where the code is on this site.

<!-- begin code provided by createblog.com --><br /><!-- begin code provided by createblog.com --><br /><style type="text/css"><br />div.blogheader, .caption {<br />font-family:Century Gothic;<br />text-transform:uppercase;<br />font-size:12px;<br />line-height:10px;<br />font-weight:bold;<br />color:#FF0000;<br />letter-spacing:1px;<br />background-color: #ffffff;<br />text-align: center;<br />}<br /></style><br /><!-- end code provided by createblog.com --><br /><br /><br /><br /><br /><br /><!-- begin code provided by createblog.com --><br /><style type="text/css"><br />table.blogbody {<br />/* this edits the other the place where the  blog is */<br />background-color:000000;<br />family-font: trebuchet ms;<br />BORDER: #FFFFFF 3px dashed;<br />width:750px;}<br /></style><br /><!-- end code provided by createblog.com --><br /><!-- end code provided by createblog.com -->

How do I add a background image inside that box? Help appreciated