For the free service, only one download at a time.
Also for the free one, they have a limit of a certain number of MB before they cut you off for a certain amount of time.
How many MB and how long they cut you off never seems to be constant though, so I can't give you an exact number.
You'll probably be able to download 2 or 3 parts now, then have to wait awhile to get the rest.
Part 3 is up, btw.
