Can't see http packets

[Ronan SAVY <R.SAVY () reponse fr>]

Hi
I would like to grab the http packet in order to have a clear view of web usage before configuring some kind of filter 
over my compagnie network.
Here is what I installed:
I have a Windows XP SP3 workstation with wireshark installed on it and 2 nic one is a nvidia nforce and the other a 
D-link DFE-530TX
I connected the D-link NIC on port 16 of my 3com 2226-SFP Plus
Behind my 3 com switch I have 5 3com baseline switches connected in cascade
On port 25 of my switch I have a Linksys BEFSX41 with on his wan my FAI modem going out on internet

I configured a port mirroring on port 16 from port 25 (I tried mirror in solo, mirror out solo, and both)
I checked that the D-link nick can work on promiscuous mode (using promqry)

When I launch wireshark from station I can't see any http traffic going out safe from SSDP protocol
I also see other packet grab from other machine on my network, packet like :

-          NBNS

-          DHCP

-          ARP

-          IGMP

Even when I browse internet on the workstation where wireshark is installed using the second NIC... I can't see the 
HTTP request going through

May be I did something wrong but I don't know what? I checked the advanced option of my NIC to see if there is Checksum 
offload option.. but nothing.

Any help would be most welcome as I have no more idea on what else I can do.
thanks

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