Right... that project isn't a "portable" driver, it's a driver for Linux, a sourceforge project claiming "POSIX compliance" doesn't really mean much for drivers.
Now, FreeBSD and OpenBSD have a kue(4) driver, each man page has a list of products implementing that chipset... Wouldn't it be easier to see if any of them wrote a driver for OS X(And then, hex editing the Product/Vendor ID?)
EDIT: Major score! -
http://www.k-micro.us/USB/drivers.htm - Looks like drivers!
USB_Etherb2.sit and Jaton_101_Enet.sit appear to be drivers for the Kawasaki LSI KL5KLUSB101B chipset.
EDIT2:
Sorry, the above drivers are for OS <= 9, not OSX.