Not sure what you mean by NIC.. I have a linksys wireless router..
NIC = Network Interface Controller, which is what you plug your ethernet cable into on your computer. Chances are, it was built-in to your computer's motherboard. The NIC is only used for the wired network connection.
In your original question, it sounds to me like your wireless is simply dropping the connection. How solid is your wireless signal and connection?
You may not notice this on small file transfers since they complete quickly (before the connection is dropped).