Apache2 shared server: default webpage [duplicate]

Greetings,

I have an apache2 server with 4 domain names point to my server's single IP address.

When I type in www.site1.com it serves pages from /home/eamorr/site1/index.php Same for www.site2.com, www.site3.com and www.site4.com

However, when I type in to the address bar of a browser without the www, it always redirects to site1.com!

i.e.

site1.com -> site1.com site2.com -> site1.com site3.com -> site1.com site4.com -> site1.com

How do I configure apache to do the following:

site1.com -> site1.com site2.com -> site2.com site3.com -> site3.com site4.com -> site4.com

Here is my default config:

ServerAdmin [email protected] ServerName www.site1.com

    DocumentRoot /home/eamorr/sites/site1.com/www
    DirectoryIndex index.php index.html

    <Directory /home/eamorr/sites/site1.com/www>
            Options Indexes FollowSymLinks MultiViews
            Options -Indexes
            AllowOverride all
            Order allow,deny
            allow from all
            php_value session.cookie_domain ".site1.com"

            #Added by EOH for redirection
            RewriteEngine on
            RewriteRule ^([^/.]+)/?$ driver.php?uname=$1 [L]

    </Directory>

    ErrorLog /var/log/apache2/error.log

    # Possible values include: debug, info, notice, warn, error, crit,
    # alert, emerg.
    LogLevel warn

    CustomLog /var/log/apache2/access.log combined

I'd like to look at the domain name and then redirect to www.sitex.com. Is there an Apache rule to do this?

I hope someone can help. My SysAdmin/apache2 config skill aren't the best.

Many thanks in advance,