You could use layout XML to remove it from all pages, then add it again for just the homepage by either using the section under
Admin->CMS->Pages->Edit->Design->Layout Update XML or by adding it to your
local.xml using the handle
In your theme's
<block type="page/html_topmenu" name="catalog.topnav" template="page/html/topmenu.phtml" />
This may have some debugging issues in regards to your custom theme. If so, turn on template hints to find the name of the file your menu is using, and you should be able to find similar layout instructions under
app/design/frontend/your/theme/layout/SOME-FILE.xml, and you can change the name and/or template file appropriately.