I've tried downloading two movies to my PC and both have failed. I'm getting really fed up with this now.
Reading on a bit more about this downloading, I found that initially I had to download something called Samsung Kies. I'm doing that now and hopefully this'll solve the problem.
Incidentally, when I entered my voucher details, the value is for £33 and not the promised £50!! It appears too that The Galaxy S is not compatible when it comes down to the available games anyway. Really disillusioned with all this.