I would suggest that you consult an attorney with experience
in trademark law. If you're in the USA (and probably elsewhere
but I don't know for certain) you can register a business name to
ensure that you are protected; the registration process involves
a search to see if any other entity has already copyrighted
the name you want. If no one else has it, you pay a fee and the
name is legally yours.
Mike is right, it's a difficult area in cyberspace just because
of enforcement problems. If you do searches on "trademark law"
or "copyright law" you'll get more info than you ever wanted ;)
Good luck!
Pat Jellison (jellison at ceps.nasm.edu)
(Who, for the record, is NOT an attorney, nor do I play one on TV.)
Good luck,