Hello Frank,
Here are the steps I took to accomplish this:
1) created subdomain dnn5.matthewfalzon.com
2) created a website for it
3) went into its website settings
4) on the first page of the settings the “Home Folder” tab, under “Folder in your Hosting Space” make sure its checked and I put in “\matthewfalzon.com\wwwroot\DNN51″.
Take a look. Let us know if you have any further questions.
Regards,
Ticket (HJY-994375)