Following the steps in the helpful codex, I have (apparently) successfully manually installed WP 3.5 (meaning I can login and view the default site theme), but when I attempt to install a new theme from the "Install Themes" window (or install a plugin from its window) I receive an error message:
Downloading install package from http://wordpress.org/extend/themes/download/platform.1.4.3.zip…
Download failed. Destination directory for file streaming does not exist or is not writable.
Advice greatly appreciated. Thank you.