NXG contains an MTS engine to allow you to use any of the hundreds of Themes available. If you want to add a theme to the list of available themes, just put the theme in it's own directory in /system/themes and the script will detect it automatically.

There is also a theme editor included. Just click the editor tab and select the theme you want to edit. There is help for every event so you know what you're editing, plus a see as you type preview to help you create the look you're after.