Hate to resurrect an old thread, but I'm seeing essentially the same thing, but on somewhat newer hardware.
Seems fair enough since nothing ever seemed to get resolved
I got minor relief by using 8178 drivers but it's not as good as I initially thought. I still get lock ups under *heavy, sustained* ethernet usage. AFAIK there are no shared interrupts in play. Luckily, I only seem to trigger the fault when backing up to another machine, so I just exit X before doing that.
I had no trouble with a single core processor and non-SMP kernel on otherwise identical hardware. If you are willing to sacrifice a core, you might try taking out SMP to see if it helps.
Haven't had a chance to try the nv driver since Xorg 7.1 came out to see if it works better than it did in the past.