Bandwidth meter / packet counter

I'm trying to use my arduino + Ethernet shield to build a bandwidth meter, preferably by directly counting packets on the network.

Does anyone have any suggestions / resources to share? I've searched the forums, and it looks like people tried this a couple of years ago, but haven't seen any concrete tips.

Thanks in advance! Julian

Whoops. Didn't see the recent posts from March - guess it looks like the arduino hardware isn't capable of this?