Tae Kwon-Do is a Korean martial art that's current form was perfected in the 1940's. The main orignisations are the International Taekwon-Do Federation (ITF, formed in 1966 by Major General Choi Hong Hi) and the World Taekwon-do Federation (WTF, formed in 1973 by the Korean Taekwon-Do Association, this is the one you will see in the Oympics).
I do ITF with the TAGB (Taekwon-Do Association of Great Britain), in Marlborough, personally think this the better one because it focuses more on self defense and sparing while WTF is more about sparing.
With belts you start at 10th Kup with a white belt, then after around 3 months you go to 9th Kup and get a yellow tag added to your belt, you then go to 8th and get a full yellow belt. This pattern repeates itself until you get to 1st Kup and have a red belt with a black tag (takes a minimum of 3 and a half years with TAGB). You are now ready to move onto the Dans where you get a black belt with a gold stripe, and as you go up the dans 1,2,3,4... you get more gold stripes.
If you want to find out more go to a club near you, and ask the instructor questions.
If you live around Marlborough or Pewsey in Wiltshire Britian there is classes in Marlborough Leasure Center at 19:00-20:00 on Wednesdays and10:30-11:30 on Sundays and at Pewsey Vale School at 19:00-20:00 on Tuesdays and 18:30-19:30 on Fridays.
Come along if you are interested, its really great fun and the people are all really nice. (The first two lessons are free so come along and try it)