In a shared hosting environment, customers cannot access or edit the httpd.conf file.
To redirect domain.com to
www.domain.com, just put this in index.htm or index.html file on the top:
<META HTTP-EQUIV="Refresh" CONTENT="0; URL=http://www.domain.com">
OR:
Create .htaccess file which contains:
Redirect domain.com
http://www.domain.com
and upload to your root content directory (usually in /www or /public_html)