what's wrong....

<?php
//common_db.inc
$dbhost = 'localhost';
$dbusername = 'phpuser';
$dbuserpassword='phppass';
$default_dbname= 'mysql';

$MYSQL_ERRNO = '';
$MYSQL_ERROR = '';

function db_connect() ?> {
    global $dbhost, $dbusername, $dbuserpassword, $default_dbname;
    global $MYSQL_ERRNO, $MYSQL_ERROR;

    $link_id = mysql_connect($dbhost, $dbusername, $dbuserpassword);
    if (!$link_id) {
        $MYSQL_ERRNO = 0;
        $MYSQL_ERROR = "Connection failed to the host $dbhost.";
        return 0;
    }
    else if(empty($dbname) && !mysql_select_db($default_dbname)) {
        $MYSQL_ERRNO = mysql_errno();
        $MYSQL_ERROR = mysql_error();
        return 0;
    }
    else return $link_id;
}

    function sql_error() {
    global $MYSQL_ERRNO, $MYSQL_ERROR;

    if(empty($MYSQL_ERROR)) {
        $MYSQL_ERRNO = mysql_errno();
        $MYSQL_ERROR = mysql_error();
    }
    return "$MYSQL_ERRNO: $MYSQL_ERROR";
}


and I got this error message

Parse error: parse error, unexpected ';', expecting '{'

From what I can see, you ended your php too early. The entire function should be scripted out, rather then ending it after the "function db_connect() ?> {", the ?> should come after your "return "$MYSQL_ERRNO: $MYSQL_ERROR";", or something along those lines. As it is now, the script knows you made a function - it simply doesn't know what to do when you call it, or where the function starts.