Aha! That clears everything up for me!
Yup, that will work exactly as you think.
You can edit your /etc/hosts file on your local machine to add an entry for undress4success.com that will "override" the official DNS entry. That way, when you go to undress4success.com in your browser, you'll go to your dreamhost site instead of your wordpress.com site. Under windows it's c:\windows\system32\etc\hosts. You can get the IP address to use by inspecting the DNS entry for your domain under "Domains>Manage Domains" in your Dreamhost panel.
What are [color=#CC0000]50DISK50[/color], [color=#CC0000]3DOM50[/color], and [color=#CC0000]1IP1DOM50[/color]?
They're Dreamhost coupons!