Then:
Yes. It is definitely possible to run multiple instances of DNN on the same server, I do it all the time. Remember that DNN is just another ASP.Net application, what you need to understand are the aspects of each instance that differentiates them apart. Do you know how to define multiple, separate Web sites in IIS? It is the same for DNN.
The things you need to keep in mind are:
1. The physical directory where DNN is installed. You can create one directory called DNN1, another DNN2, etc. Then install DNN separately to each physical directory.
2. The database. You will need to have a separate database for each instance, if you use the database in the App_Data directory this is easy. If you use a separate database instance (or a separate database server) I recommend that you name the database the same as the physical directory just to keep things straight in your head (i.e. DNN1, DNN2, etc.). If you do use a separate instance of SQL server, not the DB in App_Data, you will need to adjust the connection string in Web.config.
3. The Web site. This is the actual Web site definition in IIS. You must create a separate Web site for each physical instance of DNN.
4. The host header. This is actually how IIS determines what Web site to serve when you are hosting multiple domains with just one IP address. Each Web site must have a different host header like www.domain1.com, www.domain2.com or, if using subdomains of one specific domain you may want to do something like site1.domain.com, site2.domain.com, etc.
5. The DNN alias. This is the definition in DNN, it must match the host header definition for each site.
6. DNS. This will depend on your implementation, if the domains are already defined and pointing to the right server then everything will hook up automagically.
I think that's it, it is not a step by step procedure but those are the major aspects you must consider.
Carlos