Did you register the domain with Dreamhost or elsewhere? Also, how long has it been.
If you registered the domain elsewhere, go to the site where you registered, login and look for an option like change nameservers or change dns.....something along those lines. Change them to the nameservers sent in your dreamhost welcome email. Should be:
If you did register with DH, it should set the nameservers automatically (I'm almost sure, but not totally.) However, it can take up to 36 hours to start to resolve.
Remap sub-dir is for pointing subdirectories such as store.yourdomain.com to the directory where the files actually live, yourdomain.com/store
One more thing to check and that's to make sure your files are in the correct directory. http://wiki.dreamhost.com/ is full of good information.