Default wordpress directory issues

Hi all, I’m not sure if this ‘fits’ better in install or troubleshooting, so I apologize beforehand.

I can seemingly install wordpress (3.0.4- but I had the same problem with an earlier 2.9.x release) just fine and it seems to work, but when I attempt to install any plugins, they all fail due to a faulty Upgrade path:

Downloading install package from http://downloads.wordpress.org/plugin/twitter-tools-bitly-links.zip…

Unpacking the package…

Could not create directory. /wordpress/wordpress/wp-content/upgrade

Note that the wordpress directory path is doubled up (which is not how the site is configured). This is the same whether I use the built-in search-install method or the Upload-and-install method. Also, I can upload media items with no issues, all of the directories are similarly writeable. And yes, I’ve tried many different plugins.

FYI this is running on Ubuntu 9.10

Any insight you could give me would be greatly appreciated.