The Olympic Games are the highest goal for many sportsmen and sportswomen, therefore Olympic sailing is somehow special. There are nine Olympic sailing classes in which sailors can compete. For at most 400 people and 270 sailboats have the rights to attend the Olympic Games, each country can only send one boat to a class.
The Olympic disciplines and the corresponding classes in 2008:

Laser Radial
The Laser Radial is a popular one-design class of small sailing dinghy built by Vanguard Sailboats. It is a singlehanded boat, meaning that it is sailed by one person. The Laser Radial is a variant of the Laser Standard, with shorter mast and reduced sail area, allowing light sailors to sail in heavy winds.
Laser Radial provides the unique opportunity of sailing the Worlds favorite Olympic singlehanded to lightweight and youth sailors. Chosen by ISAF as the women youth class for all events up to 2006 and recognized by all leading nations as the stepping stone to the Olympics, the Radial is fast becoming the most competitive youth racing class with a full program of national, International, ISAF and Class World Championships supported by Class and RYA coaching.
The Radial is sailed by smaller adults and Master sailors who compete in Radial events at all levels in the full Laser racing programs from Club to World Championships
Based upon the same hull and equipment as the Laser, the Radial has a 19% smaller sail and different more flexible lower mast. Everything else is unchanged. The recommended weight range for Radial sailing is between 60kgs and 75kgs although the boat is being sailed competitively at below and above these weights.
Finn

The Finn dinghy is the men’s single-handed Olympic class for sailing. It was designed by Swedish canoe designer, Rickard Sarby, in 1949 for the 1952 Summer Olympics in Helsinki. Since the 1952 debut of the boat, the design has been in every summer Olympics, making it one of the most prolific Olympic sailboats.
It is the ultimate single-handed sailing machine that still ranks as the fastest non-trapeze International single-hander. The Finn is one of the few boats that require one athlete to be at the same time exceptionally fit and strong, outstanding in tactics and familiar with the techniques of sail and rig tuning.
Laser

The International Laser Class sailboat, also called Laser Standard and the Laser One is a popular one-design class of small sailing dinghy. According the Laser Class Rules the boat may be sailed by either one or two people, though it is rarely sailed by two. The design, by Bruce Kirby, emphasizes simplicity and performance. The dinghy is now manufactured by several boat manufacturers worldwide
World favorite single-hander was introduced in 1971. The Laser was designed as a recreational dinghy and originally known as the Weekender. Quickly the Laser established a status of the most competitive dinghy and it made its Olympic debut in 1996. It already was the biggest Olympic class in general.
470 men and women
The 470 is a double-handed monohull planing dinghy with a centreboard, Bermuda rig, and center sheeting. The name is the overall length of the boat in centimeters (i.e., the boat is 4.70 meters long).
The 470 class is one of the most widespread classes in the world. In 1976, this double-handed centerboard board was introduced for the first in the Olympic Games. The Pusan Games in 1986 saw the first women team participating in the 470 class. As it is an easy boat to handle, the 470 has become particularly popular with light-weighted sailors.
Yngling

A Yngling (pronounced “ING-ling”) is a type of sailboat that the International Yngling Association calls an “agreeable cross between a planing dinghy and a keelboat.” It is also summarized as a smaller version of the 26 foot Soling although there are differences in proportion and tuning requirements. It has a LOA of 6.35 m (21 ft) and weighs 645 kg (1422 lb).
This Olympic women’s three-person keelboat was designed in 1961 by Jan Linge. The Yngling shares the Soling’s sleek hull form, well-balanced rig, and the responsive helm. While the Yngling is not as fast as the Soling, it is quicker, and more nimble. It turns more quickly and in less distance, and the response better to crew weight trim adjustments.
Star

The International Star (or Starboat) is a 6.9 m (22.7 ft) one-design racing keelboat for two people. The boat must weigh at least 671 kg (1479.3 lb) with a maximum total sail area of 26.5 m2 (285 ft2). The Star was designed in 1910 by Francis Sweisguth—draftsman for William Gardner’s Naval Architect office—and the first 22 were built in Port Washington, New York by Isaac Edgar “Ike” Smith during the winter of 1910-11. Since that time, over 8,300 boats have been built.
The Star is the oldest Olympic class. Star was designed in 1911 and has been included in the Olympic program since 1932. After the Olympic in Atlanta the Star was excluded of the program, but late 1997 the IOC and the ISAF decided that the Star come back in Sydney.
Neil Pryde RS-X
The IOC has selected the Neil Pryde RS-X as the windsurfing equipment to be used at the 2008 Olympic Games. The main priority of the Neil Pryde RS-X is to ensure that the equipment used in the Olympics is both representative of the equipment used by most recreational windsurf today, and still performance orientated and fun in the potentially wide wind range of most Olympic regattas, ie. from 3-30 knots.
Tornado

The Tornado is the only Olympic class catamaran, with a crew of two. It has been in the Olympic Games since 1976. Designed in 1966 in England, specially to be the Olympic class catamaran., the Tornado entered Olympic competition in 1976. In 2002, the Tornado was replaced by the so-called Tornado Sport. The platform remained the same, but a spinnaker and an extra trapeze for the helmsman were added and the Tornado Sport was born. The multi-hull shape and relative large sail to a low weight ratio explain why the Tornado Sport is the fastest Olympic boat. It delivers exciting competition and challenge.
49Er

The 49er is a newer one-design class of small sailing dinghy. It is a double handed twin trapeze boat, meaning that it is sailed by a helm and a crew, the helm making many tactical decisions, as well as steering, and the crew doing most of the sail control. The design, by Julian Bethwaite, the son of Frank Bethwaite, (the designer of the popular Tasar and Laser 2 classes), is revolutionary. The boat is experiencing an increase in popularity due to its selection as an Olympic class starting with the Sydney Olympics of 2000.
In 1997 the ISAF Council adopted the 49er (two-people) as the “High Performance Open Dinghy” discipline. The 49er is a development of Sydney Eighteen-foot skiff and it is designed for high speed sailing. A speed over 25 knots is achievable. Strict one-design rules ensure the best sailors will win and the need for expensive research development by competitors.
Sources: Beijing Olympics Website, Wikipedia