vb sniffer

I need build a VB sniffer. My app is receiving UDP packets from some radio equipment with bad headers, but good data. The checksum in the datagram fails, so I think the packet never makes it past the UDP protocol layer to where my winsock control can get it. But I can see the data just fine with a sniffer. So - I just need to make a UDP port sniffer in VB, but this looks not so easy. Any ideas??

Thanks,
John