If you want to change your own DirectoryIndex to either add a different filename, shorten the list, or change the order of the list, just create a file named .htaccess in the directory where you want this behavior to occur. Inside the .htaccess file, put a single line beginning with DirectoryIndex followed by the list of filenames that you want Apache to serve first when a directory has been requested, like so:
DirectoryIndex index.phtml start.html
The above directive must be all on a single line in the .htaccess file.
Check this out
http://support.modwest.com/content/1/147/en/how-can-i-show-a-default-page-other-than-indexhtml.html