Ok in itunes (on the pc) do you have a section called ringtones on the top left? (underneath the music folder?). If not you can turn this on in the Preferences section of itunes (file - preferences?) - sorry trying to do this from memory as not at home pc at the moment.
Don't worry about the 'Purchased' folder, everything you buy from itunes gets put here, but it's not where the item is stored, just like a playlist showing you what you've bought.
To get the ringtone onto your iphone you need to sync it across. With your iphone plugged in, if you click on the ringtones tab, does it show up there to be synced? Do you sync across music to the iphone automatically, or manually drag it across? If you sync it should show up on this tab.