Have you tried registering on sky.com? your name say Joe Bloggs will be entered as j.bloggs as a user name and become j.bloggs@sky.com as your email address on skybroadband.com. You will need your viewing card number and it will tell you if there is an account already registered, if you are sucsessful then make sure you fill in all the fields including pin number etc.
If it says account alread registered then you could try using the "forgot username/password field.