How do I check to see if a name has already been taken? If it has not, how can I register it? Where can I research to see if the type of business I am interested in starting has already been created?

Full Description of United States Patent and Trademark Office: Databases & E-Resources (Library of Congress) (http://www.loc.gov/rr/ElectronicResources/full_description.php?MainID=541)