WordPress MU

Do I need a static IP address and a dot com address? I'm trying to install wpmu on Dreamhost but I get the following message after installation:
The requested URL /cgi-system/wp-inst/index.php was not found on this server.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

Also, although I get an email with user name and password, telling me the blog has been set up, when I click on the link, I get:
The page cannot be displayed.

The blog is set up here:
http://org/cgi-system/lonestarpress/
Any help would be greatly appreciated.

I have an installation on Dreamhost. I had to ask to have a wildcard DNS created by one of their Sysadmins and ask them to put the *.domainname.net alias in the Apache configuration but otherwise it was a normal install. I've never tried to set up WPMU without using wildcard DNS.

Thankyou very much. I'll contact DH and see if they'll do the same for me. No problems once you had done that? Did you have the Virtual Host option checked? I didn't - but, apart from messy URLs, will that make any difference?