I had to do a bit of research for a friend recently on exactly this topic - I hope this isn't too long but I've summarised it below and included the links I used.
Both bird flu and Severe Acute Respiratory Syndrome (SARS) are respiratory diseases.
Both diseases are zoonoses, meaning they originate in animals but are transferred to humans.
SARS and bird flu are very different.
Bird flu is caused by influenza viruses, similar to those that cause human flu. At least three of the great flu pandemics of the 20th century started as bird flu.
Bird flu outbreaks are not uncommon. Usually, however, they do not affect humans. (only birds).
Studies suggest that the prescription medicines approved for human flu viruses would work in preventing bird flu infection in humans. However, these medications may not always work.
In contrast, SARS is caused by a previously unknown type of 'coronavirus'; the same family of viruses that causes the common cold.
The SARS virus is highly dangerous to humans, whereas at present, the bird flu viruses are not.
There is no vaccine for SARS. There is also no specific antiviral treatment designed to treat Sars...a cocktail of antivirals and antibiotics appears to be beneficial if treatment is started early.
The danger in the bird flu viruses, that have been responsible for killing thousands of birds, is that it may cross over into humans , with similiar results for the human population.
Where bird flu has entered the human population in recent times the mortality rates have been as high as 50%. These outbreaks have been limited to people who have close contact with farm birds etc.
There have been at least three flu pandemics in the 20th century that were attributed to bird flu -
1918 - Known as the Spanish flu - It is estimated that approximately 20 to 40 percent of the worldwide population became ill and that over 20 million people died.
1957 - Known as the Asian flu - Although the Asian flu pandemic was not as devastating as the Spanish flu, about 69,800 people in the U.S. died.
1968 - Known as the Hong Kong flu - The number of deaths between September 1968 and March 1969 for this pandemic was 33,800, making it the mildest pandemic in the 20th century.
Here are some links -
Information from some sites provides slightly different information to that provided above - see www.cdc.gov/