If you want to preview your new domain before going live by setting the nameservers, there is a pretty easy way to do this.
You need to edit your "hosts" file on your computer.
On Windows systems (7 and 8) the hosts file is found at
Be advised that you may need to allow viewing of hidden system files.
Edit that file in notepad (or Notepad++) AS ADMINISTRATOR.
Add the line as follows:
<server_ip_here> <domainnamehere> www.<domainnamehere>
(Replace <server_ip_here> with the IP address of the web server, and replace <domainnamehere> with the new domain name you want to preview.
Once saved, restart the web browser and there you go!
More info and details can be found here