I'm afraid there are no any editors which can provide you both code and wysiwyg, because Smarty templates could not be compiled without data - you will not see anything.
I can recommend you free PSPad editor
http://pspad.com which have PHP, SQL and Smarty multihighlighter. Also PSPad has FTP client which allows to download, edit and automatical upload files to server (as from local machine) and many other useful features. It's very convenient editor for X-Cart developer.
Try to search the 'pspad' in forum and you will see recommendations from Right Worshipful Mans.