I think I have seen people pose this question before, and I found a great solution that works for me so I thought I would post.
I currently have an old fashioned html web site, but would like to develop a new drupal driven, content managed, web site. How do you develop it without taking the other one down, or having to move the drupal version when it is ready to go live?
Here is my answer:
1. Installed Drupal into my public_html folder
(I have a hosting company that sports a pluggin called fantastico that makes installing drupal absolutely painless)
2. After the installation, my public_html folder had two index files: index.html (the old "home page") and index.php (the new drupal front page). You can imagine my horror when I realized that someone going to my site would get the new completely undeveloped page instead of index.html. I tried many things to get index.html to load by default, but no luck. Either I couldn't get it to work, or I did, but at the expense of breaking drupal. Finally I came up with this solution:
3. Install the "front page" module, which lets you specify a special front page, or entry page for your website. I set this to redirect to index.html, the old main page and voila, anyone going to my website will get that page instead! When I am ready to go live with drupal, I will just turn off that feature! Meanwhile I can log into drupal by just typing the full url to drupal.