Underlying web address?

When I login through FTP I can access the files of all the domains I’ve hosted (e.g. Domain1.com, Domain2.net).

In my Internet browser, how would I access the index page of “Domain2.net” if the nameservers have not been changed to point to Dreamhost yet? I’d like to start work on the website of a domain I won’t be able to transfer for a few days.

Can I get access through some address like test.dreamhost.com/domain2.net/index.html ??

You need to create an alias (called a Mirror here) of your site: