I'm coming in late to this conversation but thought I'd chime in.
Before I started designing Open Source hardware I was a Network Engineer and was actually looking at making a networking tool before I worked on the OpenBench Logic Sniffer. Our primary goal was not packet sniffing, we wanted more of a battery powered device that could be used for various useful things. Like load up image files on a sd card, plug it into your network segment and have it serve up tftp to isolated routers. Or a target for logging that you could drop in a network segment to avoid poking holes through firewalls. It's been years since I thought about networking though and I don't remember half the things we wanted to do with it.
We were originally looking at using a Freescale MCF52233 chip which has integrated Ethernet and a nice TCP/IP stack. The project never went anywhere beyond some prototypes. Personally I think it would be possible to do what you want with an FPGA but I'm not sure it would be an easy task to do packet sniffing... General TCP tasks like tftp and such would not be too hard using Microblaze. But packet sniffing would take more work.
If you really want to pursue this I have some things that could help you out. I have an RMII Ethernet Wing design that you are welcome too, it is open source but I have just not had the time to test it out yet. It implements a ksz8041nl PHY that is capable of Fast ethernet speeds. You would probably have to build the boards yourself but it could give you a leg up to test out your ideas.
Arhi is correct in that it would be a difficult task, but the Spartan 6 landscape has changed a bit recently, there used to be only BGA options but since Xilinx released the Spartan 6 LX line there are now LQFP options for Spartan 6. In fact I have two new Papilio boards designed and currently being tested for the Spartan 6 LX chips. :)
I looked at the hackaday pictures and I'm wondering about the speeds you are trying to sample at. What is the speed of the signals you are trying to capture? Usually you want to set your capture speed to twice the speed of what you are capturing.
Try to set your speed to twice the speed of the desired signal, and also another tip that will really help is to ground the last unused probe. So the last probe that is adjacent to what you are sampling should be grounded.
I've often thought about adding pattern generator functionality as well. If you think about it, its really just doing the opposite of what we do now. The client already has functionality to generate test patterns. If we wrote those test patterns to the BRAM instead of reading from the BRAM we would then just have to figure out how to output the contents of BRAM on the Wing slot pins.
The script should automatically place it into the bootloader programming mode, but it looks like it is not successfully doing so. You should be able to jump the PCC and PGD pins on the ICSP header and then apply power. You should see ACT and PWR both lit. This will force the board into the bootloader programming mode and you can run the OLS Upgrader script. It will fail the first part but should work for the part that you need.
One other thing to consider though, by virtue of having one of the brand new boards with a 8M SPI Flash chip you are already running at the latest and greatest firmware. There may not be any real need to go through the upgrade process.
The new boards being manufactured by Gadget Factory are using a larger (8M) SPI Flash chip. The ols-loader.exe tool did not have the idcode built into its database of supported Flash chips. I just released a new version of the 3.07 packages (OpenBench_Logic_Sniffer_3.07c.zip) that includes an updated version of ols-loader.exe that should support the new SPI Flash chip.
Excellent work, I'm knee deep in preparations for Make Faire right now but I'm hoping to sneak in some time to make an official release to 3.08 with your new client. One of the cool things I'm planning to add is a Linux virtual machine for those who are having issues with drivers. It will have everything ready to go and just needs to be booted up. Also will have a USB based image so you can just boot off a USB drive into Linux with OLS drivers and software ready to go. :)
If that does not work then you can send the board to me and I will repair it or replace it. I'm located in Denver, Colorado, USA so you can choose to have Seeed or Gadget Factory replace it depending on which is more convenient for you.