$query = tep_db_query("SELECT countries_name, countries_id FROM " . TABLE_COUNTRIES);

$countries = array();

while($row = tep_db_fetch_array($query))
{
    $countries[$row['countries_id']] = $row['countries_name'];
}

///////////////////////////////////////////////////////////////////////////////////
$country_name = "Africa";
$country_id = NULL;

foreach($countries as $id => $name)
{
        if($country_name == $name)
    {
        $country_id = $id;
        break;
    }
}

if($country_id != NULL)
{
    echo $country_name . ' has an ID of ' . $country_id;
{
else
{
    echo 'Could not find an ID of ' . $country_name . ' because it does not exist';
}