"Unable to create directory [HD]/[site]/wordpress/wp-content/uploads/2011/09. Is its parent directory writable by the server?"
temporarily change the permissions on /wp-content to 775 or 777 so that wordpess can create the uploads directory.
..more info Changing File Permissions
.htaccess is a file, not a folder.
.htaccess is a hidden file(extension) by default, if it exists, you need to turn on "show hidden files" to see it. (consult documentation for features in OSX) If it doesn't exist, it's as simple as creating a new file and naming it .htaccess
option 1) Change the permissions on that file to 0666, (or 0777) and let WordPress update the file for you. Afterwards, change the file permissions back to 0644.
option 2) create an .htaccess file and simply copy / paste the code given to you by the WordPress warning message inside that file and then save the changes.
If your .htaccess file were writable, we could do this automatically, but it isn’t so these are the mod_rewrite rules you should have in your .htaccess file. Click in the field and press CTRL + a to select all.
copy and paste the code to your .htaccess file manually if necessary.
Automatically updating .htaccess