This may be in HELM (which I am currently having trouble accessing) but how do you in windows setup a default page> Are they predefined (if so, what is it?) or where is the setting to setup what I want as default page(s)?
Thanks!

You should to upload some index.html or default.asp file to the "wwwroot" folder on the server via FTP.
All passwords for email, FTP accounts and for HELM you can reset in your HELM cpanel.

I want to use index.xhtml to be my default page. How can I do that? If I use html extension, a browser won't treat that file as an XHTML document (I can't use XSL).

Please go to http://support.hostony.com and submit a trouble ticket about this.
Your request will be done during 10-15 minutes.