Well, I had to recompile support for my network card into the kernel. Everything seems to work except USB... yet the UHCI and EHCI modules load ok, as do peripheral drivers. I used the arch kernel26 pkgbuild to build and consolidate the package.
Oh yeah, before anybody tells me that I should just be using the stock kernel, or that if I can't get USB to work I shouldn't be messing with the kernel, yada yada yada - I'd like to point out that I had to recompile the kernel with forcedeth built directly in for PXE boot. And minus USB, I have a functional diskless system. Woohoo!
Here's the .config:
...and for some reason it mysteriously works after compiling OHCI in rather than as a module. I have no idea why that would be. :-/