I have seen this before! it turned out to be that nachi virus, took down 
our local whole net! (including a Cisco PIX firewall).
Try Ethereal like Travis suggested.

Travis Dixon wrote:

>On Wed, 10 Nov 2004, Hynek Cihlar wrote:
>
>  
>
>>Yes, we've tried the new beta, but with the same problem.
>>
>>But you are right, there is too many connections from the LAN side.
>>When we allow only the basic web services rejecting connections with
>>nonstandard destination ports, the problem wanishes, everything is
>>fine.
>>
>>However I don't think that this is the right solution to this. There
>>must be a more systematic approach.
>>
>>Can anyone help with this one?
>>
>>    
>>
>
>You probably have machines infected with the windows Worm-du-jour. These will
>generally cause so many connection that even commercial firewalls get overwhelmed.
>
>You should probably set up a machine with something like ethereal on the LAN side
>and look for the offending machines.
>
>
>
>
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-- 
Eric Collins
Sr Network Administrator
Tawifi.com

Downtown Tucson WiFi Network
http://www.tawifi.com