The London Guide linked to your ND web site is pretty good. Has all that you need to know, and makes sensible estimates of costs. I’d strongly endorse the suggestion in guide that you take advantage of the University of London facilities – London has many University Colleges (e.g. UCL, Kings, Imperial, Queen Mary etc.) that co-operate via the University of London. It has a great student union facility just of Tottenham Court Road, and excellent student support services (e.g. accommodation). I’m not sure if the ND facility is linked to the UoL system.
Most London students who are not in college owned accommodation will live in shared flats / houses. This works if you have a means to find others looking and hook up with them. The UoL accommodation office would be a good place to start.
I would also recommend the International Students House (big ad in guide) – it is expensive but I knew some people who got in when I was at college – a great facility and great location.
Finally, only point that I thought misleading in the guide is the plug for American Express. It is not widely accepted in the UK compared to Visa or Mastercard. If you plan to use a credit card in the UK you really need a Visa or Mastercard as well as an AMEX.