That's is strange, if you were able to connect once, you should be able to connect again using the same credentials.
Once your domains DNS information has propagated fully, you will be able to connect directly to ftp.yourdomain.com, instead of using the DreamHost server hostname (rootbeer.)
Remember, once you log-in via FTP, using either SmartFTP or the web-based client, you will initially be in your home directory. Anything you upload directly to this directory will not be publicly accessible. If you wish for your upload to be publicly accessible, you will need to upload the file to the web-directory for your domain, which by default will have the same name as the domain itself.
It is a pretty steep learning curve, but if you take things slowly and ask plenty of questions when you run into something you don't understand, you will do fine.
The DreamHost panel can seem daunting at first, due to the large amount of functionality provided, most of which you will probably never need, but it's nice to know it's available, just in case.
One panel area that you may find interesting is the 'One-Click Install' page (Goodies -> One-Click Installs). This page provides for the easy installation of many pre-made scripts, such as WordPress, Gallery 2, phpbb etc.
Anyway, good luck and have fun exploring.
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