For variable argument list in ibase_execute you can use folowing functions:
For PHP >= 4.0.4:
function db_execute($stmt,$data)
{
    if(!is_array($data))
        return ibase_execute($stmt,$data);
    array_unshift($data,$stmt);
    $rc=call_user_func_array('ibase_execute',$data);
    return $rc;
}
For any version of PHP:
function db_execute($stmt,$data)
{
    if(!is_array($data))
        return ibase_execute($stmt,$data);
    $params = array();
    while( list($k,$v) = each($data) )
        $params[$k] = '$data['.$k.']';
    eval('$rc=ibase_execute($stmt,'.join(',',$params).');');
    return $rc;
}