Hi,
If you read the article How mojoPortal Works, you will understand that default.aspx must be the default document in IIS for it to work.
You can make any page you want the home page of your site by moving the page to the home page position in the site hierarchy, but all CMS pages (pages in the site menu) are served by default.aspx so it must be the default document. Urls like test.aspx are the friendly urls but those urls are re-written to default.aspx?pageid=x
The home page of your site will work with 3 possible urls, its friendly url ie yoursiteroot/home.aspx , yoursiteroot/default.aspx or just yoursiteroot/ ( which resolves to default.aspx as long as default.aspx is the default document)
You can move a page to the top under Administration > Add/Edit Pages to make it the home page.
Hope that helps,
Joe