Possible Duplicate:
Monitor all and any internet traffic from my home PC - what should I use?
Which is the best program for monitoring local network traffic
Possible Duplicate:
Monitor all and any internet traffic from my home PC - what should I use?
Which is the best program for monitoring local network traffic
WireShark is great for monitoring all kinds of traffic on a network.
If you'd like to only see local traffic, you can use capture filters.
For example:
net 192.168.0.0/24