Listen 80
NameVirtualHost xxx.xxx.xxx.xxx:80

<VirtualHost xxx.xxx.xxx.xxx:80>
<Directory "/useroff">
    Options None
    AllowOverride all
    Order allow,deny
    Allow from all
</Directory>
ServerAlias useroff.site.ru
ServerAdmin useroff@site.ru
DocumentRoot /useroff
ServerName useroff.site.ru
</VirtualHost>

<VirtualHost xxx.xxx.xxx.xxx:80>
<Directory "/forum">
    Options None
    AllowOverride all
    Order allow,deny
    Allow from all
</Directory>
ServerAlias forum.site.ru
ServerAdmin forum@site.ru
DocumentRoot /forum
ServerName forum.site.ru
</VirtualHost>