$items = Mage::getSingleton('checkout/cart')->getQuote()->getItemsCollection();
$items->addFieldToFilter('sku', 75782007);

foreach ($items as $item) {
    var_dump($item->getSku());
}

string '75782007' (length=8)
string '32811969' (length=8)
string 'hdd006' (length=6)

$itemIds = $items->getAllIds();
foreach ($items as $item) {
    if (in_array($item->getId(), $itemIds)) {
        var_dump($item->getSku());
    }
}

string '75782007' (length=8)

SELECT `main_table`.* FROM `sales_flat_quote_item` AS `main_table`
WHERE (`quote_id` = '757') AND (`sku` = '75782007') AND (`sku` = '75782007')