<FORM action="function.php" method="post">
Имя<input class="width100" type="text" name="form[fname]"><br/>
Фамилия<input class="width100" type="text" name="form[sname]"><br/>
<input type="submit" name="submit_new_user" value="отправить">
</FORM>

if ($_POST['submit_new_user']) {
	while(list($key, $value) = each($form)){
		$value = trim($value);
		mysql_query("INSERT INTO users ($key) VALUES ($value)") or die(mysql_error());
	}
}

if ($_POST['submit_new_user']) {
	while(list($key, $value) = each($form)){
		$value = trim($value);
                echo $key.'<br>';
		mysql_query("INSERT INTO users ($key) VALUES ($value)") or die(mysql_error());
	}
}