Run WordPress on a separate section of site

If I wanted to work up a WordPress site in a separate folder, but while I am working on the “new version” of the site, I want the domain to go to the current xhtml version, how do I do that? The last time I did that, the domain went to the WordPress app., and I had to copy everything in there really fast. Don’t want to do that right now.

How do you keep the site on the “old” pages until you are done with the “new” WP site?