Not sure if this will fix your problem, but I had the same issue on my wireless network (using a WET11 bridge). This fixed it.
Go to your wet11 setup (i.e. in the browser) and turn on "Enable MAC Address cloning" (top right in my Firmware Version: 1.5.4). Hit "Apply". When the page reloads, the WET11's MAC Address will be 00:00:00:00:00:00. This is what you want.
Now start X-Link and make the X-Box look for games. You'll see the Local X-Box show up with its real MAC Address (should be 0050...). If you don't have "Enable MAC Address cloning" turned on, you'll see the MAC address of your WET11 - no good (should be, but it isn't).
It seems that X-Link disregards non-X-Box Mac Addresses when you actually connect to games. The WET11 nomination stuff in the Advanced Setting seems to have no impact on whether or not X-Link sees the X-Box. I was able to see games and connect, but it would immediately drop when I joined the game. Now all fixed. Basically, if you don't see the X-Box's real MAC address in X-link, I don't think it will work.
tedtedson <