You'll want to right click on the folder name on the left hand screen (be it wwwroot or a sub-virtual directoy if you're using it, but if you do it in wwwroot then it will apply to all sub folders i think). Go to properties, and one of the tabs is called something like default documents, and it will have a list of filenames like "default.asp", "default.htm", "index.htm" in an ordered list. All you need to do is click on add, type in the name of the page you want (in this case home.html or home.htm) and move it to the top of the list using the arrows. Then when someone goes to your directory and doesnt specify a file, it will look for files that go by the names given in that list, loading the one that it comes to first. So, if you have two files called default.asp and home.html, depending on which one is higher in that list, that's the one that it will load.
Hope that helps,