Thanks now if I wanted to let a member who has a sub-domain on our domain, "user.domain.com" map one of their own domains or sub-domains using a cname. I would need to create a ServerAlias for their sub-domain, in apache2 it would be something like below. So using the regex probably wouldn't be the best method, so just adding them as you listed in the first reply is how to go about it?

ServerName user.domain.com
ServerAlias *.user.domain.com
ServerAlias usersowndomain.com