I've tried adding
<?php query_posts($query_string . "&order=ASC") ?>
<?php if(have_posts()) : ?>
in the page.php file, with no result
Maybe page.php is not your friend for this one.
It depends where is the list of posts you want to modify.
Try index.php for homepage or archive.php for category based views.
page.php is used when an individual Page is queried - that means this page is usually the only post displayed there. Playing with its order gets boring after while .)
I just had this problem. You can see my thread here: Wordpress Posts Out Of Order after 3.1 Update
The problem is a bug in MySQL. You need to upgrade to 5.1
5.0.51a is causing the bug.