There are two ways to accomplish this; first you should check the properties
of your web site, and specify the document you want as the web page(run
IIS.msc, right-click on the default web site and look under the 'Documents'
tab in the properties - this assumes that your file is already sitting under
the default web site folder (x:\inetpub\wwwroot).
Alternatively, you can copy your file to x:\inetpub\wwwroot where x: is the
drive letter where your system is installed, and rename that file to
'default.htm' since that's the file which loads first by default. However
you most likely are going to have more stuff besides the one file, so it
would be best to create a new virtual directory under your web site pointing
to wherever the desired file is, and specify the file name in the same way
as on the default web site.