Future posts problem

I’m a newbie, and I’ve been pulling my hair out on this one.

I wanted to order my posts ascending on a page, so I couldn’t go with the generic query. I also want my posts to “age out”.

I got the ordering to work, no problem:
$posts = query_posts($query_string.'&orderby=post_date&order=asc&posts_per_page=30'); ?>

… But I haven’t been able to get rid of old posts. I tried this various ways: ‘&post_date>=NOW()’ or using monthnum, etc., but these ONLY appear to accept “=”, won’t accept a greater than, >.

I can’t use ‘post_status=future’ because I changed the post.php code so that everything would go in with a status of ‘publish’ and would show up on the website.

Any help greatly appreciated!! Vicki