OK, here is the solution to modifying the home page, esp. regarding the design of the boxes:
1. Over at the UK xcart forums, this excellent post:
http://www.xcartmods.co.uk/snippet-css-rounded-corners.html
The files affected are skin/common_files/css/main.css, skin/common_files/customer/dialog.tpl, skin/common_files/customer/menu_dialog.tpl. These file names don't all appear using Webmaster mode or Firebug, unless I'm missing some other feature.
2. skin/common_files/customer/home.tpl is used for things like your SSL cert ... you can also modify it for other things, but the 4.4 branch is now relying on other called out files. So you just have to research down the tree to find out which files to modify.
Regarding the rounded corners mod, you have to change the fill color in the css code unless you want white. Here it's changed to light yellow:
http://www.kustomrides.com/xcart/home.php
The rounded corners now appear across various browsers.