It sounds like you or someone else created an extra user/group for you called www. The standard on Red Hat/CentOS is to have the apache httpd process run as the apache user, which gets created when you install the httpd rpm. Depending on your situation and how secure you want your website to be, you can either have your content owned by apache (less secure, but then the webserver can write files easier if you need that kind of thing) or you can have the website content owned by another user and world readable. Such as mode 644 for files and mode 755 for directories leading to those files. There should be a default document root directory at /var/www/html that you can put website files in.
Just an FYI, if you are using CentOS 4, you are way behind. Even CentOS 5 is way behind and CentOS 6 should be available in hopefully a month or less (Its not CentOS's fault, Red Hat delayed 6 by over a year). If you are going to run a serious website, I'd recommend upgrading. Especially if you are going to try to run any applications with PHP. Wait for 6 to come out, which will have PHP 5.3