I just manually installed XOOPS 2.0.7.3 on my new host account because I tried to install via Fantastico, and it didn't appear to install correctly, but the same thing happened via the manual install. This same problem occurred with 2 other host accounts--one which used Auto Install from cpskins.com and the other used Fantastico.

The problem is that the modules--news, contact, forums, etc.--are not installed. Going to the Admin Menu and clicking on System Admin/Modules, I see that all of the modules are listed but uninstalled.

What could be causing this problem? Is this the way that XOOPS is installed, now, and we have to install all of the modules manually, or what?

That's correct. The system module is the only one automatically installed. You have to install the others yourself.