You can't do it by IP only on shared hosting, unless you have a dedicated IP.
What you can do depends on whether the domain is here or elsewhere now.
If it's here, just create a sub-domain such as dev.mysite.com and build your new site there. When you add the sub-domain on the manage domains page of the panel if you use the same user as the main site it's a relatively simply and painless process to switch them over when you are ready to go live.
If the DNS for the domain is pointing elsewhere (to another hosting company) then you will need to use a free dreamhosters.com subdomain and a mirror using these directions:
and lastly if you haven't even registered the domain name yet, just make a free dreamhoster.com subdomain and do it there.