I want to have products that not require to stay logged and other that need it. So i think the best way is set in the admin "Allow Guest Checkout = Yes" and when the client goes to the checkout and there's products that require the login i send him/her to the checkout.
Or maybe it's better to use an observer.
I need to know what's the name to the interceptor (or the observer).
I think ask the client to login after add determinate products may be confused, so, i want to add it just in the last point, when you push on"Proceed to checkout" after the www.test.com\checkout\cart in www.test.com\checkout, where you see the direction to the shipment.