I installed WordPress 2.7.1 manually at first, and then with Fantastico, and got the same set of errors.
The left navigation dropdowns don't work- when I click the down arrow nothing happens. My media upload buttons are also missing. I figured it might be a permissions error or something, so I tried to change the file permissions on the server.
I set everything to 777, and when I did that, I got an error 500/internal service error. This same error was reproduced on both installations I tried, doing the same things.
Does anyone know what might be going on? The host is hostgator.