It's difficult to say anything without knowing more details. But one thing to watch out for is the case in Database/Table names. If you copied your db over from Windows (which is case-insensitive) sometimes files names are incorrect on Linux (which is case-sensitive). The correct names for the files are tablename.frm, tablename.MYD, tablename.MYI. Also check the permissions.

If you are working on something that did work in another environment check mysql_error(). If you are starting from the beginning I'll second fingers99: there is lot's of good tutorials out there and the official PHP and MySql manuals are really very good.

- - Edwin