What you need to do is called "web splitting". You should be able to host more than one website within your free web space, as long as they are not too large.
Firstly, you would need to create a new directory within your web space, for example, "newdirectory", so the address of the new site would be something like:
http://home.btconnect.com/mywebspace/newdirectory
You could then point your domain name, using URL forwarding to that address. In EasySiteWizard, you could then create a new site with the above address as it's location.
URL forwarding will resolve to the destination URL (address) and display it in the address bar of a browser. If you wish the domain name to be retained, then you need to use Frame Forwarding. Please see this:
What is the difference between frame forwarding and URL forwarding?
