First of all, in SharePoint MOSS 2007, it is kind of misleading that home tab is at the same level with sub-sites in top navigation bar. It gives people impression that home tab is just a sibling of other sites (tabs), while in site hierarchy it is the parent.
When a customized page is added to any of the sub-sites and when “Show pages” is checked in navigation settings, those customized pages will be displayed in a drop-down menu of that tab. However the customized pages of home tab will not. Instead they will be listed like other tabs in top navigation bar. I guess the logic here is that in hierarchy, these pages are at the same level as the sub-sites (tabs).
I think if you really want to put these pages in home tab’s drop-down menu, you have to customize that top navigation bar control or the master page.