Taxation and hand luggage rules are completely unrelated to each other. You should be able to take your laptop as cabin luggage, either in your bag - for the cheapest airlines - or next to your bag - for legacy airlines, which probably includes most transatlantic flights. The latter is what's usually called "personal item".
But taking the laptop as a personal item does not mean you can import it tax-free. If it costs less than EUR 430, you can import it without any formalities and you don't need to declare it. If it costs more than that, you'll have to declare it and pay VAT (and possibly customs duty but VAT is usually the big one for something like a laptop).
Also note that other goods you might be importing also count towards the allowance.