Geiri I do not beleive vbulletin uses the PHP mail command
Are you sure your php mail command works has your host tested this?
As far as email what email do you not get? Have you turned on all things to test like admin notification of new uploads? You have set the correct send from address in global options? You have viewed your email spam filters to ensure they are not getting misplaced?
Thats an individual server email setup thing. We define the from email when passing email to the mail command but seems your php has to have a default setting your host can assist with that or simply yes you could edit our pp-inc.php file and add something like this under the error_reporting line at the top of that file.