Hi Lars,
Do you need to install any files and folders on the country specific sites like web.config, default.aspx or all mojoportal folders and files?
No, the whole idea is to use a single installation and one set of files. Your host may not have it easy for you to configure it correctly to do that from your control panel so it may be best to ask them to help.
If you were working with full control of the server it would only require 1 IIS web site and just adding the host headers for each domain to the single site. It "could" also be done with multiple IIS web sites that all point to the same physical folder but this would lose some of the benefit of a single site because each separate site has some overhead for memory.
Then in mojoPortal you assign the domain name/host name to the site you want to use for that domain and mojoPortal will resolve requests for the domain to that site. Any unnassigned domains will resolve to the first site which is the master site.
Hope that helps,
Joe