I can further confirm this. I tried several methods to register my free account on a Virgin Media ISP, and all failed. I then went to my friends house who uses BT internet, and it worked perfectly. So its definatley an issue with Virgin, but once you create the account you are ok to manage it and play on Virgin internet.
Can't explain why, and I wouldnt advise actually contacting Virgin Media on this matter as I am sure they are unable to resolve it in any reasonable amount of time. If you have this problem, just use a friends computer with a different ISP or go to an internet cafe or something.