Assuming you have this rule enabled 24/7 it will block everything from the Vista PC that wants to go to the internet.
Incoming traffic mostly is an "answer" to packets that have been sent out by a PC in your LAN.
Since your Vista PC isn't able to send packets into the internet, there will also be no incoming packets.
Additionally, if there are packets incoming which cannot be associated with an already established connection, they'll be destroyed (dropped or rejected).
So to answer your question: If outgoing packets are blocked there should also be no incoming packets