Disconnecting broadband from nic

I've just moved from dial-up to broadband for my internet access.

To reduce the risk of attack whilst I'm not using the internet I would like
to disconnect the pc from the network without unplugging it.

I was using "winipcfg" to release my connection when not required.

After installing "NetMeter" I've noticed that although I release my IP
address all UL's stop but the DL count still continues (albeit small, also
I'm sure if this count goes towards my download limit).

Is there any way I can disconnect/disable the nic when it is not required?

Ted