Bigfoot Networks has just released drivers for their Killer NIC cards to fix the compatibility issue with GFWL.
You can pick them up here: http://www.bigfootnetworks.com/support/index.php?_m=downloads&_a=view
188.8.131.52 for Vista and XP 32 bit.
Let me just say that these guys rule. No, I'm not a paying customer, no I'm not being paid to say nice things. (I wish!) I'm a writer with not one, but two review copies of Killer NICs (M1 and K1) who wanted to be able to play Halo 2 and Shadowrun online.
Bigfoot found the issue, and even though it wasn't really their problem, they patched in a fix in their drivers so that Killer owners could play these games. In less than a month. Hell, in 15 days. That's awesome.
Now, if they could give NVidia some lessons...