You can embed navit in to ways: you can make navit embed itself by setting NAVIT_XID. Navit can also get "pulled" by using a corresponding function of your project (e.g. void QX11EmbedContainer::embedClient(WId id) for Qt 4.4).
Here is a gtk sample to embed navit's window into you own window: http://libgarmin.sf.net/zfe.tgz
See also Dbus to learn about the brand new dbus interface.