If you are receiving 403 error message after browsing your domain than check the Apache error logs.
root@admin[~]tail -f /usr/local/apache/logs/error_log
[Tue Nov 17 19:38:32 2009] [crit] [client 192.168.0.2] (13)Permission denied: /home/admin/public_html/.htaccess pcfg_openfile: unable to check htaccess file, ensure it is readable
As per above logs it seems that the nobody user is not getting read and executing permission upto any of that folder.So make sure that the public_html and the subdomain are set read and executing permission for nobody user.
