I'm assuming you are using a SCORM package for your captivate quiz to talk to Moodle. If that is the case, you need to turn off navigation in the settings for the SCORM package. In the setting of the SCORM package, go to Appearance > Show more > "Display course structure in player" should be set to "disabled" to hide the navigation.
Strange, you don't have an option to disable like in the picture below? What version of moodle are you using and what version of SCORM are you publishing to via Captivate?
Scorm 1.2 and Moodle 2.0. Should I upgrade to 2.5.1? Here's the screenshot.