Ghosted: a ghosted page is one that is read directly from the site definition
on the filesystem.

Unghosted: an unghosted page is one that is read from the SharePoint database
and *not* a physical file

When you create a New SPS Site, All The pages Will not be stored in the
Database.
Instead It will refer the Pages in the File System under \60 folder. These
Files are called as Ghosted Pages.
Once If these pages are modified and Saved then It will Store the Modified
pages in the SQL DB. These Pages Are called UnGhosted Pages Which will pass
thro' stsfltr.
Unghosted Pages Can be retrieved only thro' Front Page 2003 And thro' Portal
Only. Otherwise You Can't See the Pages.

For More Ref. U can Go Thro' the Articles,
www.bluedoglimited.com/.../ViewPost.aspx?ID=4
(Or)
www.codeguru.com/.../

For finding pages programatically,
blogs.msdn.com/.../400661.aspx