I run numerous joomla sites on Dreamhost with no problems, and I'm willing to try to help, but I need more information.
What version of Joomla are you running?
DId you install yourself, or use DH "One-click"?
What editor are you using in the Joomla Backend?
Running PHP as CGI, or apache-mod?
If you inspect your DB via phpMyAdmin, can you see the "new" content you have added?
Your problem could be several things, including directory permissions, but it is really hard to tell from your descriptions.
Could you provide a url, so we can see the site. You might also consider installing JoomlaXplorer (spelling?- a readily available joomla/mambo file manager) to enable you to see things like permissions on directories and files.