dodger,
Use the html validator at
www.w3.org to see your errors. Not much you can do about sponsor codes producing an error but the rest should be easy to clean up.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd"> is the correct dtd. You can read up on them at w3 also.
