I have to make use of a domain like http://mycompany.inventory.com with my website. How can i set this?

if you work with multisite, you are able to enable subdomain using the following establishing wordpress-config: find out more here: http://codex.wordpress.org/Create_A_Network

define( 'SUBDOMAIN_INSTALL', true );

or try wordpress mu domain mapping plugin. tutorial are available here: http://www.wpwebhost.com/2009/09/using-multiple-domains-with-wordpress-mu/