I guess its possible. Some basic pointers to how its done on apache.
basically, you define the several websites to point to one set of tiki files. In apache, this can be done through seperate VirtualHost blocks or using the ServerAlias parameter. I guess using IIS there is something similar to a ServerAlias. Where a website can listen on more than one hostname.
Then in the local.php, you write some scripting, there are examples on tw.o that basically looks at the _SERVER environment variable SERVER_NAME or HTTP_HOST depending on your webserver and sets the database user/pass and name accordingly.
Simple but highly effective.