Additional to the note below:
If you're using the "SHOW FIELDS" syntax, be sure that you're adding the table name instead of the db name in the "FROM" parameter:
<?php
$result = mysql_query("SHOW FIELDS FROM table");
?>
Also possible:
<?php
$result = mysql_query("SHOW FIELDS FROM table.db");
?>
or this:
<?php
$result = mysql_query("DESCRIBE table");
?>
http://dev.mysql.com/doc/refman/5.1/en/describe.html