There is nothing built in to replace the file with. If you wanted a table with rounded corners you would have to customize the template yourself to achieve that. I did mine with images inserted into a 3x3 table. Here is an example of my shop(still under design) if you want to see it
http://www.thecrackedbook.com/xcart/customer/home.php. There are some pretty good tutorials on the net. Do a Google search for rounded corners and you'll find them there.