I don't have alarming 20 second page loads on your site either, so this might be the path between you and dreamhost. i agree with ronthai that you could improve performance by tweaking image sizes.
tracert is one of the tools you can use to confirm or deny a problem along the route.
in windows open a 'cmd' window and type 'tracert yourdomainname.com'. It's a little difficult to cut and paste from a windows cmd window, but if you need help understanding the results you should google for the steps to copy from a windows cmd window and paste the results in this thread.