Sounds like you have done it correctly. Are you going to premiumyarntest.dreamhosters.com in your browser? That's how you will have to view the site until you make your DNS change at godaddy.
Thee are two other tricks that you can use to be able to view the file in a browser using the premiumyarn.com domain name, both are documented in this wiki article (which I'm guessing you have already seen, if you got that far with correct step): http://wiki.dreamhost.com/DNS_-_Viewing_site_before_DNS_change Scroll down to the section "Changing your hosts file" or "An Even Easier Technique: Switch To or Add DreamHost’s DNS Servers!"[hr]
Actually I looked more, it looks like the DNS for premiumyarn.com has already been changed to dreamhost.
I'm getting the same sitte at both premiumyarn.com and premiumyarntest.dreamhosters.com and looking up reverse DNS shows the site is being served from apache2-rank.chertan.dreamhost.com
That said, your mileage may vary. DNS propagation takes time, and not everyone gets the change at the same time as the change propagates across the internet. If your still getting the old site at premiumyarn.com try to force a broswer refresh with Ctrl-F5, If that doesn't work you need to wait and try again in 12 or 24 hours.