I edited wp-admin/includes/post.php
I edited line 805@
and line 841@:
$q['posts_per_page'] = 15;
If you change both numbers to the number of posts you want to view, it should work. I've tested it live on a 2.7.1 WP blog with 100, then 150, then 250 posts per page. I tried to get 1500 posts per page but that crashed the admin. 999 posts per page works. Best to find the number that suits you, 1000 may not be the maximum.
Hope that helps.