Restricitng categories by Custom Post Type

Hi,

I am trying to limit the amount of thinking that content managers will need to do when adding new content to the site. I am using custom post types to group all the posts that will be on each page of the site. I am then using both the custom post type and categories to determine where the post is being displayed on the site.

I would like to limit the categories that the user has to choose from in each custom post types to just those which are actually used by each custom post type.

So it would be like this:
Post type = Home Page
Categories that are shown when in the Add New Home Page post screen : Cat1, Cat2, Cat3

Post type = About Page
Categories that are shown when in the Add New Home Page post screen : Cat4, Cat5, Cat6

does anyone know of a way to do this? Thanks for any help.