>Is DEFAULT.HTM always a direct mapping to an IP (I mean, is it a standard), or >is this just the way my web host has it set up?

One thing I would add to what Randy told you, is that this is not a mapping to your IP, it is simply a default document for any directory.

www.somedomain.com/index.htm
is equivalent to:
www.somedomain.com

but so too is:
www.somedomain.com/subdir/subdir/index.thm
equivalent to:
www.somedomain.com/subdir/subdir/

Think of the IP as the unique Internet name of a computer, the DN as an alias for the IP, and everything after .com as a path to a document. The web server just substitutes the default.htm if you don't specify an actual document, but instead give a path ending with a directory. If you omit the path altogether, the web server gives the default document (/default.htm)

HTH,
Bill