Learning ISO - how not to do it

So I am new to all of this digital SLR lark. I am the proud owner of a new Nikon D90, thanks to the recommendations of many, including Blip's own wingpig

I was at a the birthday party of a friend and was lucky enough to meet a chap called Simon Helson. I had taken my new toy to the party in order to experiment with portrait shots and the low light conditions of a typical flat party.

I am still finding my way around the camera's functions, and around the subtleties of photography (having grown frustrated at the limits of a point-and-shoot, but having no clue what the hell I am doing when it comes to f numbers, iso settings, and whatever else lurks in the many options I now have at my disposal).

Simon was kind enough to give me a quick tour of the basics of ISO settings, not to mention the benefits of investing in a decent flash. I've uploaded an image of Simon taken BEFORE this tuition, hopefully it will serve as a lesson to me in the future. Especially when it comes to understanding both ISO settings and the benefit of setting exposure weighting area to spot.

Ah well.