Josh,
I got a very quick response from Dreamhost; here’s the problem: I chose a One-Click SIMPLE Installation instead of a Custom Installation. The Custom Installation will give you permission to change themes, whereas the Simple will not.
Here’s what you have to do:
1. Remove your One-Click install. Follow this link for instructions on how to do it: https://wiki.dreamhost.com/How_to_Remove_a_One-Click_Install
2. Once the blog is deleted, you need to create a new blog using the Custom Install. Follow this link for instructions on how to do it: https://wiki.dreamhost.com/How_to_Install_an_One-Click_Install
I’m currently waiting for the confirmation email to come from Dreamhost, so I can’t tell you if that will solve it, but hopefully it will.
pete