The way I did this was to create a file in the directory above my public_html (www) folder called 'dfiles' (for download files) then went back to the file settings and started to add '../dfiles' (without quotemarks) and submitted, if it didnt work I changed it to '../../dfiles' and so on until it found the file by itself, if you keep changing the place where you think it is supposed to be, as well as changing the location of where you want drupal to look it will be very difficult to find, if you keep the 'dfiles' folder in the same directory tree (usr/dfiles/public_html(www)/store/admin/files' then it will find it eventually, all you really have to do is keep adding '../' until it finds it, if it goes out side the straight line directory then it will be more difficult to find it.

Hope this helps.

Jimmy (also a noob!)