Im something could be done.

something has been done

Cool. Whats the program that enables and disables the NIC, and I can download and use it?

Something like that is possible. I found out by accident when I had a dual boot set up Windows/Linux. At the time, some early hibernate functions were being developed for Linux. I hibernated my Linux setup and just by chance decided I was fed up with it and deleted it using Partition Magic to grab the space back for Windows.

Booting back into Windows, I found that the NIC card no longer worked because it had been turned off. It took quite a lengthy bit of research via a spare machine to discover how to turn it back on using a DOS boot disk and the card's ancient utilities.

I imagine it depends on the card though.

Why would you want to do it though? It's easy enough to stick on a free firewall and just turn off all internet connectivity when you want to. And if you only had the card enabled when you were sending data you'd never be able to download or receive a reply.

Oh, and you don't need to download anything. Device Manager/Disable Device

the most sensible way of doing it, as Peter has told you twice, is use a firewall. lets all your net traffic out and also lets in any you've requested while blocking any you haven't

you could also disable the NIC manually in the control panel

or you could physically disconnect it - my dad pulls the phone wire out of the wallsocket whenever he dosn't want to be online, thay way he knows it's only connected when he wants it to be