Possible? Search only posts, exclude pages

I made it work by changing the file:
wp-includes/query.php
When it says: (line 836 on a wpmu 2.6)
$q['post_type'] = 'any';
It should say
$q['post_type'] = 'post';

Wondering if there is a way to do this by not editing this file. I mean by using a wp hack in the header, or in the search template. if anyone knows the proper way to do it, please tell me here.

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