Web sites are configured to load certain default pages since URLs don't usually have that page in them. You never see http://www.amazon.com/myform.aspx
It is a configuration option in your web server. What web server are you using? Is it IIS?
In IIS you can specify a search order for "default" pages and it allows you to add others, like you could even add myform.aspx and your web server would search for that page. I'm not sure if a .NET project has to have a default.aspx page or not.