I recommend WebkitGtk. This is the renderer that is used to power Safari, Chrome, and a number of other browsers. It supports rendering SVG as well as HTML.
Just apt-get install libwebkitgt-3.0-0. You can try it out by running /usr/lib/webkitgtk-3.0-0/libexec/GtkLauncher.
You can then use whatever language/bindings you like to build a GUI around the SVG renderer, including Python's Gtk bindings: http://www.aclevername.com/articles/python-webgui/
Here's another good article about building desktop UIs using Webkit and pygtk bindings: http://arstechnica.com/information-technology/2009/07/how-to-build-a-desktop-wysiwyg-editor-with-webkit-and-html-5/
