The Default.aspx page is created by SharePoint when the site is provisioned.
Using FrontPage 2003, you can create a Default.htm file in the root of your
SharePoint site. Put whatever content you like on this page including a link
to the Default.aspx page. However, the .htm file will be stored in the
SharePoint database, not on the hard drive. IIS is setup by default to
display a Default.htm, if it exists, before a Default.aspx. The home link in
the Top Nav of your Site should still work because SharePoint uses a fully
qualified URL rather than just a slash to represent home.