To activate virtualhosts write, in the end of the httpd.conf :
NameVirtualHost *
And after that you can add virtualhosts with this syntax, just make sure the dns names points to your servers ip:
<VirtualHost *>
Documentroot /home/subdomain
ServerName subdomain.cyberfamily.dk
Serveralias www.subdomain.cyberfamily.dk
ScriptAlias /cgi-bin/ "/home/subdomain/cgi-bin"
</VirtualHost>
Documentroot , tells apache where the .html files will be
ServerName , tells what name apache should call itself when a users requests a page from the virtualdomain
Serveralias , tells apache an alias for the vhost, for an instance www.
ScriptAlias , tells apache where to find cgi-scripts for vhost