It's been a little while since I've done it inline even more so when using a Windows box to capture, more used to using managed switches and spanning ports.
However, from memory, what needs to be done is as follows :
(1) Bridge your two network cards
If I recall, this is a simple as highlighting them both, right clicking and selecting "bridge interfaces".
(updated -> in the text that was here before I said to configure bridge itself with IP settings.... technically it should work without because most of its magic is at Layer 2 rather than Layer 3 .... so try without extra bridge config work first)
(2) Start a wireshark capture
Hopefully wireshark will let you watch the virtual interface, otherwise you only need to watch one interface, it will pick up on all traffic.
Let me know if you need more detail, although I might pop back an update this post later.
Last edited by mixture; 14th October 2009 at 18:28.