You will have to contact the administrator to make the change for you. You obviously can not use .htaccess files on a Windows server.
As a temproary solution, you can create a html file with a meta refresh tag that will link to the default.asp page. Something like:
<meta http-equiv="refresh" content="0;URL=default.asp">
<body bgcolor="#FFFFFF" text="#000000">
I will try and look into the possibility of using the Global.asa file to accomplish that and get back to you. The Global.asa file is somewhat the Microsoft version of the much more powerful .htaccess!