Read this for starters:
http://answers.yahoo.com/question/index;_ylt=AjPYT7xFoPyzTgfyB3IEFLQjzKIX;_ylv=3?qid=20070918212333AAkTsBX
http://answers.yahoo.com/question/index;_ylt=Agv9Wgw_njIQWEf0jbmTl3YjzKIX;_ylv=3?qid=20090615172248AAe8Xz8
http://answers.yahoo.com/question/index;_ylt=AjWhxtRQe_27cqVyR4XfzCgjzKIX;_ylv=3?qid=20081013154653AAH0C9I