If you haven't donated, 15 simultaneous downloads are the maximum. Donators have 100 (I'm not sure if the 200 mentioned in the "Downloading Rules" are still right). Already the lowest donation step is enough to get the donator status for the account lifetime.
Sorry now I am a little more confused … the limit of 100 or 200 is that not the number of downloads in a day that one can do (I have 150), but it does not say if the number of of downloads that you can do at the same time is increased. I am also confused with "account lifetime" I thought I read that a donation is only good for a 30 day period on an account?