Network activity monitor

For a long time now I've been looking for a simple network activity
monitor for Windows. What I want is a monitoring tool that would
quietly listen in on all traffic in a segment and log all ports,
except those I've deemed "safe". That's all. A log would look
something like this:

<timestamp> <source_ip> <source_port> <target_ip> <target_port>

I more or less know what kind of traffic I should have in my network,
so I'm not interested on ports that I expect to see (21, 25, 80 etc).

I know you can use apps like Snort to do this, but it's kinda
difficult to sieve out the required information from it. All I want is
something to catch my attention to unusual traffic. I'm just about to
start writing such an app myself, but if you know a product that does
what I want, please let me know.

Thanks,
-- Rubio

Rubio