configure service desk plus with IIS

configure service desk plus with IIS

Hi,
 
Could someone please tell me if it is possible to configure IIS in server 2008 to automatically load service desk plus without having to list port externally?
 
ie, when going to helpdesk.domain.com it would take you to http://servername instead of http://servername:port?
 
I currently have helpdesk.domain.com pointing to server IP and then under default website I have it pointing to http://helpdesk.domain.com:8080 which then loads the service desk.
 
But I want to have it clean so it loads as an actual sub domain without the need of ports?
 
Thanks

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