Directory permission problem.

I can install WP but if I try to import posts or to upload an image, I get:

Before you can upload your import file, you will need to fix the following error:

Unable to create directory /home/treacle/public_html/wp-content/uploads/2010/02. Is its parent directory writable by the server?

Surely, this should be sorted by the installation script?

Which file is it suggesting does not have the correct permissions and what should they be? Also, should they be recursive?