Want to see who is congesting my bandwidth

Want to see who is congesting my bandwidth

I have my 1mbps connection speed crippled suddnely. I want to see whose pc on the netwokr is generating a lot of traffic [b/c virus or something] and disable the pc switch port/quarantine it. under normal time, the bandwidth is quite enough. witht the LAN isolated I get the right speed on my laptop. I have 2801 router and 3750 switches, one of the switches port is the gatway to the LAN users. I want to monitor Internet traffic only. how can netflow help me with this. Looked at the demo and am at a loss, any help or docs to read ?
thx!

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