I added a contact form to the footer. Apparently it works fine in the main page, but if I go to any of the categories, lets say myblog.com/category/, the contact form is looking for submit.php at myblog.com/category/submit.php. Where I should put physically submit.php in order for contact form to find it in any category page?
It depends where you contact form is... if (As i imagain) its in your template folder you can use this to create an absolute path to it:
<form method='post' action='<?php get_bloginfo('template_url'); ?>/submit.php'>
If you places your "submit.php" in the top folder of your hosting account you should use the same but without the "template" like so..
<form method='post' action='<?php get_bloginfo('url'); ?>/submit.php'>
To help you understand:
<?php get_bloginfo('template_url'); ?> = www.domain.com/wp-content/themes/yourTheme/ <?php get_bloginfo('url'); ?> = www.domain.com
Hope this helps. Cheers, Sagive