Here is an alternativ .... Exclamation Wink

If you running on Apache (Who is not in these days ?) setup your DNS with a wild card as well i.e

*.domain.com 123.123.123.123
mail.domain.com 123.123.123.123
www.domain.com 123.123.123.123

In your httpd.conf file edit your virtual host section like thi 
see also http://www.apache.org/ for details if you are new to apache

Code:

<VirtualHost domain.com www.domain.com>
ServerName vhost.domain.com
ServerAdmin webmaster@domain.com
ServerAlias *.domain.com    <--------------This line makes it
DocumentRoot /usr/local/etc/httpd/vhosts/domain.com/htdocs
TransferLog /var/log/domain.com.access.log
ErrorLog /var/log/domain.com.error.log
<Directory /usr/local/etc/httpd/vhosts/domain.com/htdocs/urchin>
AllowOverride All
AddHandler cgi-script .cgi
DirectoryIndex index.html index.php index.cgi
Options FollowSymLinks ExecCGI
</Directory>
</VirtualHost>


Now every URL *.domain.com will be resolved in your DocumentRoot
i.e. user1.domain.com / user2.domain.com / user3.domain.com